The same thing happened with a Guitar Hero guitar of mine when my girlfriend spilled her drink on it during a night of drunken wailing. I would press the buttons and they would stick for a second or two; it was unplayable for the GH and RB games as you can imagine. I had to take it completely apart and wash the keys and this plastic mat they pressed up against in warm soapy water. Once everything dried I put it back together and it worked like a charm (still works, I passed the set off to a nephew last month). YMMV with a controller.
BTW my dog chewed up my sticks on my dualshock but they still work fine four years later.