Sound Checks on Walkman WM-4

I've got myself a WM-4 from ebay, in more or less alright nick. Opening it up to check an issue with it's potentiometer a belt snapped. I've now replaced both belts with new ones, and had a quick look at the potentiometer problem.

I am now stuck on a sound quality issue along with the volume meter problem. I only listened to it for half a song before the belt snapped initially, so I don't know if it's my tinkering or a consequence of the Potentiometer. I've cleaned the head, pinch wheel and capstan system, but not demagnetized yet, though I doubt this is the issue.

The potentiometer is spinning round and round instead of the set limit it's supposed to have, and clicks on or off jumping to random volumes and channels. What is it's part number? does any one have the Manual for the WM-4? Would it be worth finding and using contact cleaner on it?

I would love any advice you have. Regards