My 1950 jd a powertrol works ok but will not stay up even with no weight on 3 point. So far I have changed the oil ( I used 30wt non detergent oil). Dummy plugs are installed. Today I pulled both check valves and lapped them to be sure of a good seal. I'm not sure where to go from here. When I got this tractor, it had a loader on it that also wouldn't stay up But the rock shaft was not in use so I didn't think much about it. Am I looking at pulling the valve housing next? Also, where can I get parts for powertol.