At least for me, I much appreciate when people post detailed and interesting things like this, so no need to apologise for making a great long first post! That might end up being invaluable to someone else searching in the future. I'd have been completely stumpted many times, if not for people taking the time to document what they do.
I wish I had the energy to write this much anymore... day job takes most of my time nowadays, actually doing synth/programming work takes the rest, and I've gotten a bit disillusioned with online communities anyway.
Anyway, I have never opened up my AN1x, although I should because I have a v1.04 ROM waiting to be installed (not that it probably matters much) - and could do with checking the aftertouch trimmers as it's quite over-sensitive. I suspect it's going to be horribly dusty in there when I do...
I've previously done a large-scale cleanup operation on a neglected Yamaha V50, which was supplied in rather disgusting condition, and it uses the same rubber-controlled keybed. I believe from memory that Yamaha codenamed it the LC keybed. It goes way back to the DX21 and co as far as I recall. My V50's keys are still yellow, and I really should have used DeOxit or something as most of the buttons are VERY temperamental... but it works 'enough'...!
Thanks for the good post!