I have taken the part that the buttons are attached to and cleaned all four sides of each and every button on tw0 60 II's with a qtip... but you should hit it with some canned air too while you have it open... its not too hard...
These switches are a sealed variety and not easily cleanable. They only cost about .22 cents each, but the job will require simple soldering, and ofcourse disassembling the mpc. I just ordered some last week!