I can't find the thread about the radio/cassette/CD player that worked for a while after I jiggled the on/off slide switch and then stopped, and then jiggling wouldn't make the power light even flicker in the slightest. But that tended to convince me the problem was somewhere else.
But just before I left, I figured there was nothing to lose so I took the knob off and sprayed just a little bit of the stuff in the top of the slide switch. The can was blue and red or something that reminded me of WD-40 but its name was nothing like that.
Anyhow the radio went on immediately after turning it on, no jiggling required. So WD-40 looks pretty good for cleaning the contacts on a power switch, probably carrying 12 volts.