I have a Altoz 72" rotary with a weak Hydro-Gear 4400 left drive. The right seems fine. I have changed the filters, fresh oil, and followed the air purge process in the manual a couple of times. The left drive has no power and will only move the mower with a lot of coaxing. It also makes a lot of "growling" noise like it is going over relief. It seems to operate better in reverse. While I have done a lot of hydraulic work, I am unfamiliar with this model. My first thought is the "pump" inside is worn and/or the drive motor side is and oil is leaking past the surfaces. I do not trust the local shop and Altoz does not offer any kind of shop manual. The troubleshooting guide in the Hydro-Gear manual does not cover this kind of problem. Any thoughts? It is an expensive mower and I am not against putting in a whole drive but I want to be sure if that is the easiest way to go. Thanks.