[Radioroslyn]

Well unsolder it and carefully pry up the tabs that hold on the cover. Once you get the cover off spray the innards with DeOxit. Try this for starters and see if that does it. If not you can drill out the rivets that holds the switch to the cover. After you get it apart use a lite abrasive to clean up the switch contacts.Get some small screws from the hobby shop to put it back together. You may find the contacts are badly burnt that's time to find a new pot/sw.
Good Luck/w it
Terry