Replace the sail switch. It's cheap. If you aren't comfortable dealing with gas and electric, bring it to a technician. Not quite so cheap...but better than dying.
No reason to clean it; just replace it. Removal depends on the unit. My furnace
involved screws in the front, going into the cabinets, the propane
connection coming into the side, wires coming into the other side, then just pull straight out to separate from the exhaust tube.