Finally gotten around to test driving the machine. The blade goes up and down really slow, the hotter the machine is the slower it goes. If you raise the blade up it leaks back down at a rapid rate. The fluid and filter were changed with 30 weight and no difference. There is a lot of play in the linkage. You do not hear the relief valve when you raise the blade up. The cylinders were rebuilt around 1000 hours ago. Any idea on where to look for the problem and could it be a bad relief valve in the pump.
Run a pressure test on the system. Problem is there is no good place to tap in. You'll have to disconnect a hose and rig up some fittings. Should make 1000psi at 1200 engine rpm for the #46 hydraulic unit. If you can't lift the pressure relief valve there is a good chance the pump is worn out. It is about 55+ years old if it has never been changed out.