Fran's right! Try to find a person who can work on it OUTSIDE of Yamaha. You're clearly out of warranty so it's your choice on who services it.

Fran's also right about Roland too. I've got a busted key on my old dusty Roland RS-70 (wife's stupid cats).., and I about crapped my pants when I contacted Roland for the repair. The repair for them wasn't replacing that single key.., but saying it would be easier to just replace the entire keybed. The cost was more than half the value of the synth. Even if they repaired teh single key.., cost would still have been damn near half the value of the synth. I have no clue how to fix them so.., well scotch tape is a beautiful thing