I have a 721 Grasshopper that has 1000 hours. The left hydrostatic transmission does not have any power reversing. It will barely move the mower backwards. It, however, seems to be just fine moving forward. Is this just the process of the drive going out or is there something else I need to check that could be causing the problem. I just recently changed oil and filters on the transmissions. I checked on price of new hydrostatic transmission, about $1100. Are there kits I could possibly buy and repair myself or is it required skilled workmanship? Any suggestions are appreciated.