Replace volume pot

Marakanetz, It looks like it is not straightforward but rather some convoluted combination of Volume and Balance with addition of Phono. I wouldn't touch it with a stick.

As for technicians - it is different (from designer) set of skills. Technician should look for faulty or misplaced component or open/short circuits but should not modify circuit under any circumstances (worst kind of technicians) since it is designer's job. Designers on the other hand don't have enough troubleshooting experience to find problems efficiently and to apply proper fix. So, when you talk to techs about circuit modification remember that they don't do it (or at least shouldn't).

Well, whoever 'wouldn't touch it with a stick' wouldn't be able to restore this unit at all weather it's straightforward or not. At least to me it was, is and will be.
I have an engineering background, but being more of a hands-on person(and lousy student too), chose manual labor vs. calculations or designing digial logic circuits. So there's almost no traces of designer left in my skills, although can still build DIY class A solid state amp or single-ended and push-pull tube amps(similar to guitar ones). Speaking of logical circuits or processors, I've done it only in my dreams:-)

Marakanetz, I can attempt to help but have to see schematics - at least of this section. I built my first amp (100W tube 2xEL34) when I was about 15. Later when electronics became my profession I lost interest and now prefer buying instead of building. I spent best half of a day inside. Sometimes I thing work outside would be better for me (in spite of money).