I have been cleaning thr boards and contacts with electric component spray (like thr WD40 electric contact cleaner) and if its "vegitated" those old boards will take a light wire wheel cleaning. I polish with Brasso as well if its pitted or really discolored.
I swear, i have yet to have a bad switch, once cleaned they have all worked well. The variable WW switch was a bear as you need to desolder a piece to get it apart safely, but all the rest have been relativly easy to restore.