The Go-To electrical contact cleaner
(Aside: Seriously, can one describe this product as "enjoyable"? It's just not an applicable term, like, is transmission fluid "enjoyable"?)
As a collector of vintage electronics, I use Deoxit D5S6 (and other Deoxit products) regularly. Use it before resorting to taking apart delicate (i.e., old) switches. It also improves connectivity with household plugs and switches, but use sparingly. "Knock offs" of Deoxit just don't seem to work as well and as long in my experience. If the spray does not work, it's back to careful disassembly of the item and judicious use of needle files...very time consuming but necessary.
For bulky, robust electrical connections, consider almost any brand of dielectric gel.
Finally, once while driving an older car, the ignition switch stopped working. Just by coincidence, I happened to have Deoxit in the trunk. A couple of quick sprays, allowing time to evaporate, and the car was on the road again. So, it's mechanically useful, too.
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