imported post
The best way of course is to open the switch and clean it if you can. We used to use carbon tetrachloride but they banned that after someone grew a third eyeball in his forehead or something like that.
Contact cleaner is available from any electronics supply house, including Radio Shack. Clean 'er up and re-apply a bit of dielectric grease and it will be good as new.
Some people use WD40, and it works ok, but doesn't have the right solvents in it to clean the corrosion, etc.