I am about to propose what some here will consider snake oil. Had this not worked for me on numerous occasions on cars and other applications I would not mention it. It is not guaranteed to help your problem, but it can't hurt.
I picked a vintage Sansui receiver out of a trash bin at work. Also grabbed the beat up set of speakers that went with it. Sure enough, it powered on but had the scratchy potentiometer syndrome like most of these old receivers develop. Since I had $0 in it I decided to see of there was a cleaning agent I could buty that would fix it. After some research I found this:
Deoxit Fader F5
This variation of cleaner is safe for use on plastic potentiometers like those found in guitars and old receivers. So it's safe for use in just about any application.
Took the cover off the receiver and sprayed down the controls while working them back and forth. Voila, the receiver worked like new.
Fast forward a few months and I was struggling getting a scoter running for my Niece. Replace a bunch of parts to no avail. As a last resort I took all the connections apart and sprayed the connections with the Fader F5. Put it back together and it ran perfect.
My Camaro would throw the ABS lights intermittently. Before I tried anything else, I pulled the connectors and sprayed the contacts with Fader F5. Not more ABS lights.
Also used to fix a sticking door switch on my microwave.
The connections might look perfectly fine, but there can be a very fine amount of dirt/corrosion that prevents a good contact. I'm not saying this will fix the problem, but if it were me, it would be the first thing I would try.