Contact cleaner was my first thought too, I’ve used it successfully to unstick potentiometers like volume knobs.
In this case, depending on the source of the failure, neither that nor the silicone spray might be sufficient. There’s probably a spring in there which could be stuck or partially rusted from moisture (in which case a selective dose of WD-40 would help, followed by some form of lubrication). I’d try to take the cover off and take look at the mechanism first.
Contact cleaner was my first thought too, I’ve used it successfully to unstick potentiometers like volume knobs.
In this case, depending on the source of the failure, neither that nor the silicone spray might be sufficient. There’s probably a spring in there which could be stuck or partially rusted from moisture (in which case a selective dose of WD-40 would help, followed by some form of lubrication). I’d try to take the cover off and take look at the mechanism first.