残念！
One question, have these keys gotten heavy use? In other words, do you think that it is due to wear or just age?
I did open my Tau to fix it; details: Eigenharp repair thread
But, that was not to fix the keys and I only had to disturb the board for the percussion keys. I did not notice any difference in calibration but it could be subtle.
Based on my experience, your keys will be very hard to get to and you have high risk of rendering the rest of the instrument unusable. So it’s probably a last resort to attempt a fix yourself. Even then, though it seems theoretically possible from the code to develop a write-only trial-and-error recalibration procedure, the hurdles to figuring that out in the future are quite high.
A lot of us would be interested if you get a response from Eigenlabs. They’re well made but can’t last forever.