07-30-15: Ptss
From the front of the switch?
No, not from the front. Contact cleaner won't be effective unless it reaches the contacts.
Also, if the housing of the switch is completely sealed, with no slots or other small openings, spraying it from inside the preamp won't accomplish anything either. In that situation probably all you can do is to toggle the switch up and down many times, and see if that helps. If it doesn't, the switch would probably have to be replaced.
Best regards,
-- Al