Yamaha SY-1 Strange Behaviour

After mostly restoring my Yamaha SY-1, I seem to have one last problem that I can’t seem to work out.
It is somewhere along the signal path of the PWM, which is connected to a whole bunch of sounds, such as the Sax, Piano, Double, and Reed.
These sounds seem to be intermittent, and I’m not sure if its a coincidence or not, but they seem to work better (sometimes come back completely for a few minutes) if I mash the keys really fast and wiggle the PWM slider - could this be an issue with one of the transistors within the PWM circuit?
Another thing I’ve noticed is, some sounds like the Harpsichord, Double and Reed are much quieter compared to the other sounds (whereas other videos I have seen of the SY-1 in action show these sounds to be a consistent volume as the other sounds.

After a few days of tinkering, taking out the transistors from the PWM circuit, checking them on a breadboard and confirming that they work, then putting them back in, and still having the same issue with the whole PWM signal path only working intermittently - it wasn’t until I decided to go back to checking all the connections to the PWM slider and switch that now for some reason the synth seems to be fully working without any dropping out at all of the sound. I even turned it off and left it for a few hours before turning it back on. I even went through and adjusted all the sliders, knobs and switches. Seems like there was never a problem in the first place.

Looking back at what I had done at the beginning, which was replace the slider with a temporary pot - that made no difference.

Right now my current theory could go back to the PWM switch being dirty (maybe the gunk inside the switch was blocking the connection, but earlier in the week I had cleaned the switch with Deoxit, and confirmed that all the connections were working). The only thing different I did this time was really struggled to pull off the switch cap so I could take it out - did pulling on the switch improve the connections inside it?

Also, when the sound came back, it wasn’t immediately after my last bit of tinkering with the slider and switch. It happened just like always, starting out with no sound, then I had to constantly play around the keyboard for a bit (and constantly adjust all the sliders and switches) before it would come back after about 10min. Except this time it seems like it will stay this way…for now…