The PO said they were torn down and rebuilt? IF that's the case, if new fluid/filter/bleed doesn't cure it you may have to pull it apart and make sure it looks OK.
Clean, clean clean the case before you pull it apart, clean work surface. Take lots of reference pics during disassembly. Watch as you open the case, if memory serves there was a wild *** spring in there, lol. Mine is a 2006 as well, Toro, so probably quite similar to my wheel motors.
