Whenever the switches have gotten to the point of being unresponsive I've pulled them out and scraped the carbon deposits off of the posts and dimples on the underside of the wing-shaped thing.
I've always wondering if I should file the tops of the posts down in order to remove the pits as well and if "yes" what happens when the posts have been filed down to nothing ? (Buy new switches, right ?)
The other thought was to use solder to fill in the pits on th posts rather than file them down.
But I usually end up just putting the switches back without doing either but I thought I'd ask what other people do, in preparation for the next time.