Took my 1986 L455 Diesel version into my woods for a quick job and of course at the very furthest point on my small acreage away from the barn the hydrolic drive on the right side stopped working completely. I checked the linkage, it is ok. It won't move either direction, so I don't think it's a relief valave? Also I'm sure the chain is ok, I can feel resistance when I rock the tires. Any suggestions? Thanks, George