The goldflash contacts have a life cycle as well. After almost 40 years the used-to-be smooth surfaces have banged into each other 100s of 1000s of times. Gold being soft, it will get worn and misshapen, leading to intermittent response. At that point the switch is bad and should be replaced, so you're not losing anything by running some 2K grit across the points instead of a dollar bill or similar. It might last a while, might not.