Hello, I've only just read this post.
Fill buttons not working or sticking is not acceptable, but if you can't get these fixed can you connect one of those 10 way Yamaha pedals to a Psr2000 and use those to trigger fills and variation changes instead of fighting over faulty buttons?
Diki is also correct, dirt and dead skin from your fingers, dust and cigarette smoke especially if you are out playing in a club can soon damage your expensive arranger so cover it up when not in use.