Mickey2

Is it the button type bakelite controller? (rectangular shape). Two of my machines has this pedal and sticking hasn't been a problem. The parts involved should be simple enough to sort out, at least in theory. A good cleaning should help. Is it the square button itself sticking, or some of the metal-spring parts underneath? You can brush a bit of teflon grease on the joints and parts related to the spring action, but don't get anything on the copper parts since the electricity runs through them.

Cari-in-Oly

You can also wax or polish the bakelite parts. I had one controller that the button would stick so I took it apart, cleaned and polished the button and the housing where the button comes up through it.

QuiltsRFun, any other controller won't fit in the knee lever bracket, it has to be a button controller.

Cari