bkay, does it feel sticky? or does it feel like the button slides easily and just too muck pressure needed? I have used Happich Simichrome polish for cleaning and polishing the Singer controllers and even a T&S case. It makes them look really nice. I know it is supposed to be a metal polish, but it works really well on the plastics that I have tried it on. I'm thinking that once you get the controller apart the button looks like just a little squarish cup. I would make sure there is not lint and dirt on it or the opening in the base. Steel wool to clean the metal contact areas.
(Thank you for comment on "get-together" thread. I know we miss or forget some of the things talked about.)
Janey - Neat people never make the exciting discoveries I do.