DO NOT USE CONTACT CLEANER! First, the pot is hermetically sealed, therefore contact cleaner will not work. Next, Contact cleaner can adversely affect other components on the printed circuit board, some of which could produce some really bad results. The best advice I have is to replace the pot. If you cannot do this one yourself, have it done by someone that can.
Jim, I've had a pair of 3000s since they first came out, which I believe was early 2006. Never, in all those years, with thousands of jobs, had a single button or potentiometer failure. I did, however, have a 1/4-inch foot-pedal jack and a USB Host connection go bad on me a couple years ago.
Good Luck,
Gary