Looking around it seemed like a very high proportion of Sony’s MiniDisc drives have this single point of failure around a drive belt. Hoping that sharing the info helps someone else in future :)
I have recieved a reply from Tascam support who state:
I am ordering a selection set of belts to see if I can find the right one through trial and error.
I dug out my old Tascam 564, to try and transfer off some recordings I made in the 90s, but the drive would not work anymore. I unscrewed the device to take a look and saw that the belt for part of the minidisc had become too loose.
Does anyone have any idea of what kind of belt I would need...