rtvinnacombe

My lawn tractor just stopped moving. The motor runs but the transaxle will not move at all. Belts are good, linkage is al moving as it should. The unit is discontinued by the manufacturer and the replacement unit is now discontinued. I do not see nay place on the unit to even check fluids and there are no visible leaks. There are two check valves on the top of the case but they do not appear to be service ports. Does anyone have any information of how to fix this one? The tractor is old but has been working well until now.