Sony TC-654-4 drive motor slowed

[brschu]

So, I was just in the middle of moving some 1981 superfine recordings into MP3 files, and my machine - TC-654-4 - just then decides to run 2/3rds of a half-note slow.
Does anybody know how to understand if my motor might be going, and how to repair it if it is?

 

[Vintage Texas]

Could be the tape-travel path is gummed up from the actual tape (dry tape syndrom)
If the heads and tape guides are clean, the capstan-motor or power-supply board can have problems.
Does fforward + rewind works fine or slow in both directions ?