Funny, I just fixed two pads with this problem earlier today. They go bad with disuse, but are easily cleaned: gently clean the run & select contacts on the PCB with cotton swabs and isopropyl alcohol. Don't rub too much, because the q-tips seem to erode the contacts after a while. Then, very gently, clean the little black circles on the under side of the rubber. I've had success with dry or barely damp q-tips (alcohol is bad for the rubber). I've restored my TG and SNES start and select buttons countless times this way.