After serious thinking Brian Gaff wrote :
Switch cleaner is not as good as wd 40, its not a conductor thing its a
mechanical thing. If you can get a tiny bit of the old sewing machine oil
inside and assuming its not gummed up with polish then try that.
Brian

WD40 is extremely flammable, even the waxy remnants of WD40 can be
triggered to catch fire by the arc of a poor connection. Switches are
not expensive, just fit new ones.