Etherwave Standard: Searching for Solution to Demolished L6 Coil (Horror Story?)

Hi all, this might be a bit long for my first post but I'm hoping you can help me.
A "quick, short" (horror?) story and then my actual problem at the end. 

The Preceding Events

Roughly 20 years ago, my dad got an Etherwave Standard theremin for his 30th birthday, played with it a bit and couldn't ever get the hang of it, so it sat in a closet or on a shelf untouched for a relatively extended period of time. However, despite the dust on it, it seemed to be in pretty good condition when we plugged it in, and although we lost the plastic tuning tool (!!!) and the manual with time, we have the original charger for it and it seemed to work quite well as I've started down the path of learning how to play it.

I had been watching videos to learn techniques on how to play it and primarily came across Carolina Eyck's videos (from like 10 years ago) where she not only talks about her playing technique but also talks specifically about the Etherwave Standard, and recommended I pick up the ESPE01 mod (which I have ordered, and just arrived conveniently days after disaster). My plan was to get that mod installed and then practice, but my curiosity and excitement got the best of me and while I waited for the mod to arrive I went through reading, watching, and learning things about the theremin, and I came across this totally brand new concept of zero-beat that I'd vaguely heard of before but hadn't fully metabolized into real knowledge.

We recently picked up the Stylophone Theremin and it was through the experience of playing with that that I started to actually understand what zero-beat is theoretically supposed to be, which please correct me if I'm wrong, is when the theremin stops making noise if there's nothing around it's tuned pitch range (which I've been imagining like an invisible sphere or maybe a cylinder around the antenna). I decided that I'd plug my theremin in and route it to a tuner so I could experiment with how the default range was and just generally learn a bit more about it, and somewhere in my head it clicked that no matter where the pitch knob was, the theremin would never reach zero-beat. So, I made the totally correct and accurate assumption that it needed to be tuned internally.

I scoured the internet looking for a version of the manual that would be more accurately centered around the operation of this particular model, and found one that seemed to be an exact fit, with the PCB's serial matching as the 11-211C. So, I prepped myself for following the instructions for tuning the pitch according to the manual.

Methodical Disaster

Little disclaimer, I'm not experienced with electronics. I tried to get into it in the past with some arduino starter pack and a robot arm kit, but those were unfinished projects that I never really got too deep into despite wanting to, I'm much more of a software developer type guy (because developing software doesn't cost as much).

According to the instructions, I'm supposed to do the following:

Using a clip lead or a temporarily-soldered wire jumper, connect the two leads of C28 together

I couldn't find a clip lead, and I don't think I used a wire jumper but rather just... a wire that I very carefully and meticulously cut into a very small piece and soldered to both sides of C28 which should be even easier to remove, and although my solder skills are super novice I think I did a decent job with it. I still don't know what C28 has to do with any of this, since the manual never makes it clear on why to do this, and doesn't even say anything about removing it after you're finished tuning, which is interesting...

Anyway, after that, it says:

Then connect the instrument's audio output to headphones or a monitor amplifier. Now follow these steps to adjust L5 and L6:
1. Set P1 (the Pitch Tuning control) to its mid-position.
2. Grasp and hold the pitch antenna with one hand. With the other hand, adjust L6 for zero beat. Note: If the slug in L5 is fully counterclockwise, you have to turn it clockwise a turn or so in order to hear zero beat.) Then carefully turn L6 counterclockwise until you hear a pitch of about 3kHz (3-1/2 octaves above middle C.

I plugged my Theremin into my interface for my computer and went to a site for tuning that I could use to get the actual kHz from, so I could try to get it exactly (or close to it) to 3kHz. I turned it on and got my tuner ready.

I prepped my tool for adjusting the L6 coil.

A metal... magnetic... 20mm hex screwdriver nib.

How was I to know that the inside of the coil was practically the same material they use for the Wooly Willy magnet toy, you know the one, where you can pull the metal shards up to give the bald face a mustache?

I started adjusting the L6 coil, and at first it seemed to work, but I didn't know which way to turn, I didn't know how hard to turn, and I didn't know how soft the material would be by comparison. I heard the pitch range change, I heard a moment of zero-beat, but I think the magnetic metal element I was using to tune it was interfering with it, and so I wouldn't have been able to effectively tune it regardless. As I pulled out the nib, bits of the ferrite core stayed attached to it, and an orange-brown color saturated the metal.

Despite my better judgement, I decided that obviously it was this magnetic metal nib that I was using that was the problem. In hoping that it wasn't too destroyed, I looked for a non-magnetic allen wrench that fit the size, and thought I found one but was too stupid to even check if it was magnetic first, which it was. The added length didn't help the issue, and after a little longer of fiddling and turning and trying, the Theremin was dead and the surgery was a complete and absolute failure, with only myself to blame. I had seen some random post on here talking about using an allen wrench with a comment to it that said something along the lines of "I'd be very careful, wouldn't wanna damage the coil, plastic is better" and I assumed that just meant "be gentle" but no. No it does not. It means use plastic.

Unfounded Confidence

So here I sit, looking over my demolished L6 coil, realizing how deep of a mistake I made, but confidence got the best of me. I told my dad I'd fix his Theremin (although I guess it's mine now), and that I was absolutely positively sure that I could find a replacement component to that specific coil on the board, and get the actual plastic piece I need to properly tune it. So I wrote down the writing on the side of the coil, SLOT TEN-5-10 CCTI 0627, and got to work searching for the part.

This brought me to Coilcraft, where I discovered that they discontinued that series, and according to some posts on this forum, that was likely because of some RoHS compliance stuff, maybe I got lead poisoning? I don't know?

No biggie, though, I'm sure that their newer Unicoil series would have a suitable replacement for it, right? I just have to read the data sheets and find the matching numbers, right?

Not right. The data sheets don't match up, according to an archived version of the SLOT TEN series datasheet (that I found here: https://datasheet.octopart.com/SLOT-TEN-5-10-Coilcraft-datasheet-10791220.pdf), SLOT TEN-5-10 was tested with a frequency of 2.5MHz, while just about any of the 10mm Unicoil inductors were tested at 40MHz. I did my best at trying to figure this stuff out, but it's an entirely new area to me, and all of the AIs I talked to told me that these things weren't just a calculation away from having a potentially matching number, as the test frequency would theoretically change the level of inductance in a non-linear way.

So, I took to the support line of Coilcraft, first leaving a message with their tech support team who are apparently all working from home, and then using the form on the site. I asked if they knew of an equivalent, or close approximate, that would work as a replacement for this part. Here's what they sent back to me:

Unfortunately, we do not have an alternative (or close) to that discontinued product.

The core is no longer available, and we are not aware of alternate suppliers for it.

I've since hung my head in shame, regret, disappointment, and a feeling of utter betrayal by an ecosystem I thought for sure would have replacement parts for older electronics. Perhaps the specific part used in the Etherwave Standard was only ever used by the Etherwave Standard, I don't know.

It makes no sense to me why this part would fall off the face of the planet. Either way, I live and die by this mission.

Finality: The Mission

I believe I have the following options, one is about time and energy, one is about networking, and one is more about experimentation.

1. Time and Energy: I'm still doing this. I can try to find another manufacturer somewhere, or some warehouse with the specific SLOT TEN-5-10 inductor still sitting there after so many years. Maybe I can find something somewhere with a close enough match to the inductance chart in the datasheet that I can try to install.

2. Networking: I'm doing this right now. I can post to any place I find that seems to have a high concentration of Theremin professionals, or even a chance of there being one somewhere lurking in the shadows. I've read that there's this mysterious Thierry guy that hangs out in these forums that might know a thing or two, although I'm not trying to downplay the help of anyone else. Maybe someone here knows a specific place that can repair it, or a specific sketchy Chinese manufacturer that might sell the component. Since I got the ESPE01 today, I also went ahead and emailed Wilco to see if he can help. I might cross post this to the /r/Theremin subreddit, or any other place I can find.

3. Experimentation: I'm considering this more and more as I run into dead ends. I stated earlier that my background is in software development, and not in electronics, so I don't normally deal with the limitations of the laws of physics on a low level like this, so I'm sure I'm making plenty of assumptions that could be completely wrong, but... Would it be possible to:
  3.1. Not listen to the Coilcraft Senior Applications Engineer and just go for one of the lower inductance coils and see where the chips (or I guess the pitch) falls?
  3.2. Purchase some ferrite and fix the coil myself? How hard could it be to replicate an industrial process, ha ha...
  3.3. Replace the circuitry of the L6 coil with an arduino and program whatever non-linear input/output it was supposed to do. Maybe using some sensors? Maybe trying to measure how the other coils react and model that reaction in software?
  3.4. Go step by step in replacing the components of the original PCB until I have something that works with the modern and available components?
  3.5. Just straight up build a whole new PCB that fits inside of the box and uses the knobs and antennas?

That's all I can come up with to solve this particular, heavily disappointing problem.

So, we've come to the end of my cautionary tale. Either I will find a solution, and this will no longer be a horror story, or I will live the rest of my life feeling like I destroyed something so priceless that it couldn't be repaired. The Etherwave Standard will remain on a shelf, like the faded husk of the unicorn I hit with my car. One thing's for sure, I will continue on this path until I find a solution, whether it's the piece itself, or the witch/wizard powerful enough to help me revive this unicorn.

And then I'll install the ESPE01 mod and learn how to play using Carolina Eyck's cool one-hand-octave technique.

Thank you if you read this or even just skimmed it, if you're able to help or not, I really appreciate it. If you think this counts as a horror story then please don't forget to warn your children, I have a feeling it's going to become more difficult as time goes on to solve this.