I too have tranny problems with my Sears DLT 2000.  It has 125 hours on it (which I believe to be really low) and its kaput!  I pulled it off and broke it down and found nothing burnt, broken, galled, or snapped.  Oil was kind of dirty so I soaked everything in a parts washer and cleaned it up.  After everything dried, I re-assembled and filled with new oil.  I think that it needs to have the air bled out of it, but I don't know how to do it.  Has anyone out there purged one of these Hydro Gear units before?
Thnks