comments:
Are you comfortable with a screwdriver? Sounds like you need to crack her open. Looks like you've got a service manual available online here:https://www.scribd.com/document/495942669/PC-1250-PC-1251-Service-Manual I'd take some time, read up, familiarize yourself with how everything fits together first. The exploded views start on page 16 and are helpful for knowing what to expect from a mechanical standpoint but make sure to pay attention to what screw went where still. Get contact spray for the controls. You can go for DeOxit if you wanna get fancy or get some generic stuff on the cheap. You spray it into the slider, slide the volume a TON of times, it flushes out the crap in the slider and cleans up the oxidization which takes care of the oxidization. Something like this, electronics contact cleaner:https://www.amazon.com/CRC-05103-Electronic-Cleaner-11/dp/B000BXOGNI As for the sound, there's a fair chance you've got stretched belts.
Cleaned the movement with this https://a.co/d/00SU7x0I Everything else with dawn dish soap.