I have a 1993 Bobcat 753 that I just purchased. The unit operates properly for the first ten minutes or so. Once it warms up the right motor does not want to drive in reverse. It will go forward fine and the left motor cotinues to function in forward or reverse. Since it works OK for the first few minutes I don't think it is linkage? The hydraulic fluid looks like it is actual hydraulic fluid. The manual says it will ron 10-30 or 10-40 motor oil in the hydraulics. I also thought that it may be a problem with one of the replenishing valves. What I can't figure out though is why it works cold but not once it is warm? Any thoughts or suggestions would be most appreciated!