My 1990 Cub Cadet model 1320 lawn tractor stopped moving this summer. I discovered the belt that goes to the hydrostatic transmission assemby was off of the rear pulley and chewed up but not broken. The plastic fan that is above the rear pulley was down to only two fan blades. I ordered a new belt and fan and later some STENs hydrostatic transmission fluid. In the process of removing the battery, battery mounting hardware, fan and chewed up belt I discovered a fill reservior on the transmission assembly favoring the left rear wheel. It had high and low fill level markings on this reservior and my fluid level was below the low level mark so I bought fluid and filled it to just below the high level mark. The tractor runs, drives, and mows again and has more power in reverse when going up an incline than it ever had since I bought it new.