Quoted from Milltown:Pinball recourse sells,a very cool socket cleaning stick.
Amongst other usefull tools.
+1. I also use the stick. If you hold the socket button from underside while you twist inside bottom it cleans it well. I then twist the stick in an oval pattern to clean sides. Every once and a while a socket gets loose and wont ground. A dab of solder at the base will fix that.