The switches burn pretty good inside so even a used one that is working might not work for long. They are not too hard to take apart and clean with 600 or 800 paper.
It is possible to put them back together backwards, so mark the orientation of the body parts when you take them apart.
The bits inside do like to fall out and get lost, so do this on a bench where you can collect anything that escapes.
Silicone dielectric grease, or even wheel bearing grease or vaseline will work to hold the inside bits in place when you reassemble.
Make sure to clean the center rocking contacts as well as the round contact points.
The seat switches can be refreshed in the same way but have more springs and ball bearings that escape when the switch is disassembled.
Good luck,
-Joel.
