Hi, I have a 1978 or so L-425. I started it one day and the left side drive started driving MUCH harder than the right side. just a little push on the stick and it would REALLY go. i used it like that a couple of times and the last time it just stopped moving all together. right side works fine. pulled the drive motor and checked it out and all looks good. pulled the bypass valves and checked the winch valve and all good. any ideas based on failure mode? thanks in advance!!