toro wheel horse transmission fix or repair

[bmwpartsman 0]

I have a toro wheel horse hxl mower model # 71191 and serial 5910817.It has a tranny made by hydro-gear with these numbers 92-9790 and 5206t1301.It appears that the transmission has stopped working I have opened the unit and nothing seems to jump out at me as far as I can see but I'm no professional transmission tech. Is there a common issue that this unit has? Or perhaps know of a used replacement Tia