I hope this isn’t too late to be of use, but I did open up my Tau trying to get it to work again, which I wrote about here:
The first point is, because of this calibration issue, any opening of any Eigenharp is a great opportunity to publicly document as much of the internals as possible, so kudos for those pictures! With enough information, some problems might be able to be solved without having to open a “virgin” instrument. If yours is still open, I second Mark’s request for more pictures 
Second, when I did finally get the Tau working again, I did not notice any calibration problems and the keys seemed to respond as before. I was very careful to avoid disturbing anything relating to the keys but if you read the above thread, some was inevitable. There could have been a small change that was too small for me to notice though. Based on the Tau board, I can see how differing pressures on it (e.g. slightly different torque on screws while reassembling) could cause small deflection differences on individual unloaded keys that could be compensated for.
I’ll end with a question, have you or anyone else made contact with John lately? If there was one message in a bottle I could get across, it would be to please open as much of the remaining engineering details as possible (protocols, instrument and basestation firmware, etc) so that we diehard fans can get the most mileage out of them.
The next best thing would be to be able to get them repaired and/or recalibrated but I’m not even sure if anyone has been able to do that recently.
-Josh