Sounds like a dirty contact, and the switch generally would not require replacement to fix. Go to Radio Shack and buy some contact cleaner. Spray copious quantities into the offending switch (you can do this from the top, without disassembling the switch), then exercise the switch several times. I did this with mine about four months ago, and it has been fine since. This is a fairly common problem. The switch may eventually require replacement, but I would try this first.

Phantom