Guess there are 2 ways you could attack this, #1 carefully take everything apart, neatly lay out all the small parts on a white sheet of paper and carefully clean, polish and re-assemble each individual switch. Probably the rite way to fix things. Or #2 , get a small can of contact cleaner with a small straw nozzle and a white rag, spray in and around those switches as much as possible while catching any excess cleaner in the rag. THen do the same with some WD40 while working the switches back and forth. #1 will probably involve a whole afternoon and a fair amt of aggravation, #2 about 20mins? and it just mite work????
I fixed alot of stuff with WD40 and a rag:fingers-crossed-emo
Craig