Wow, was it almost a year and a half ago I did my last entry about this? Time flies!!!
Well, I removed my Poly-61 from a table I have kept it on while working on it and put my Matrix-6 there instead and plugged it in just to see how it was doing.
I noticed all the keys were still working, except two, which I think I knew about but forgot. Good news at least that they're not getting worse again like on the Poly-61...
Also, I took the opportunity to install the two replacement keys I ordered from http://sounddoctorin.com/synthtec/parts/key.htm. They are actually Korg Lambda keys which lack a small tab that pushes the rubber contact down but Bob kindly glued some wooden piece there instead and they seem to work just fine! :)