I am currently working on a Technics RS-M63.
It's not a high end machine, and seems like it could be easy to work on.
At first I thought it had a belt issue, but I took off all the panels and took a deeper look.
Seems to have a pinch roller issue. The pinch roller isn't fully engaging with the capstan.
You can play the videos below with audio to hear what is going on.
I have no real experience in fixing anything like this, so I'm mostly going in blind, but I have been watching a lot of various Youtube repair videos.