I'm not sure if this is already common knowledge or not, but there is new amazing firmware available for the xwhatsit controllers. I just stumbled on the
enormous deskthority thread about the new Model Fs and some firmware fixes that went with it. After skimming through it, near the end I learned that DT user pandrew has created a beta of the QMK firmware that runs on not just the new keyboards and controllers, but the original IBM models (including the F122) and the xwhatsit controllers where it replaces the original firmware. It supports the F122 standard, ISO, ANSI, and all pad layouts.
All I can say is after years of constantly fighting with my F122's threshold values (phantom keys, unresponsive keys, inconsistent performance with temperature, etc) I was seriously contemplating finally giving up on my F122 and selling it off as "not working" because it was a lemon. I figured it was either the backplates, or the way it was bent, or not enough tension, or grounding problems, or possibly it needed a bolt mod. Nothing I ever did improved the performance. It felt and sounded amazing, but a keyboard that I couldn't type on is a (very) expensive paperweight that made me depressed every time I'd look at it.
The QMK firmware totally changed all of that for me. pandrew's firmware breathed new life into my F122. It uses a totally different method of auto-calibration where it auto-calibrates the the keys into multiple threshold groups and adjusts things dynamically eliminating the issues with the "one size fits all" method the original firmware used. The concept behind it is that a simple on/off threshold value is insufficient to work reliably with the capacitive sensing as the values shift across the keyboard layout and with environmental changes. It was also found that the always on/always off pads were very different in terms of their threshold values than the real pads with flippers on them, so they were essentially useless to try to calibrate against.
I believe it also brings improved debouncing and denoising routines compared to the original firmware. It makes the xwhatsit and the F122 work like it always should have and like it deserves.
If you have a restored Model F with an xwhatsit, you definitely should check this out. It now has a permanent place on my desk again.