Check The Bypass Valves on Eaton Gemini 771 Hydrostat Transaxle if There is Loss of Drive. 

These are no longer made. There are many still out there in use. The biggest problem is as repair parts run out no more are being produced.

I have a 771 my right side on my woods. Mower is leaking at the very bottom of it, but it's not a hose. It looks like it's coming out of the casing at the bottom. Do you know anything about Any Common problem with them Leaking