I too had a 4010SL back in the mid 70s. That was my last RTR deck. I never had problems with heat in the reel motors so whatever it is, it isn't normal. I would suspect that the reel motors have bearings that need lubrication. There were "Permanently Lubricated" bearings, but I can't say if that is what Teac had. If so, those might need disassembly and relubricating.
High frequency response is the first thing to go as heads wear. There could be some adjustments in the playback electronics that would restore the HF response, or not. Do the cymbals splash rather than sizzle? No shimmer after the cymbal is struck?
Speed inconsistency will present itself with sustained notes.