Just a thought, but the motor shaft itself needs occasional lubrication. Just talked to Mike at VPI about this, re my older model TNT, and he recommended using 40 weight oil VERY SPARINGLY, via one of those needle-applicators, beng sure you don't get any oil on the pulley.
Also, for some time the pulley does occasionally seem to "lock up" and not turn without a gentle push, especially since I got my SDS. But the push always gets it going. At least so far. Good luck, Dave