"All clues that lead away from a mechanical issue, I think"
Not really. Or at all. Temp and humidity can do weird stuff too. As can the missus painting her nails in the vicinity and the reactive phenols from that depositing on everything within cooee.
When you press another key you induce a tiny vibration. Consider what you are proposing as the alternate, namely that there is 'a device or mechanism' that the software is able to trigger and cause random keys to stick down. Changing the software polling rate is A COINCIDENCE. You are sitting there, warming the thing up, rattling it, offering up bodily odors and the like. Some of this stuff will change the microcosm of the keys environment.
Only real q is exactly how to best clean the sucker. I would probably try working each key up and down a few times while holding it across to each side and see how you go then, should work - as long as the sticky stuff is on the stem not the bottom as then it will just 'tack on'.
This is basic logic, what you do with it, well...
