Quoted from HowardR:
Sorry but I have to disagree.
As to the first, properly adjusted switches will almost always stay clean and working for years. To the second, bank and motor switches are prone to being jarred by untrained fingers and accidentally moved out of adjustment, causing new problems. Even normal relay switches can suffer from attention from untrained fingers.
With that said, d-gottlieb, if you have a maintenance routine that works for you then I wouldn't want to tell you what to do, but for others with less experience, I highly recommend only fixing what's broken.
This ^^^^^^^^^^ x 100!
If you are new to EM's I guarantee that if you go and clean/adjust every switch in game you will make things worse. As @howardr says it is much easier to fix what is broken! Why clean 100's of switches and riskj making things worse when you actually only need to find the one switch that needs attention and deal with it.
I do appreciate that sometimes it may be necessary to go through all the switches if you don't have a schematic and have come to a halt in troubleshooting. However, usually enough info can be gleaned from schematics of the same era in order to point you in the right direction. There is lots of help on Pinside...I personally enjoy the challenge of trying to pinpoint the faulty switch and love to help others when I have the schematic available.
BTW my first game ever was Jack in The Box that I purchased back in 1983 - I remember using contact cleaner I mean why wouldn't you right!? Thankfully the machine didn't catch fire.... but I sure was lucky!