The machines sometimes left the plant with a extra valve, for a field install of a ripper/4x1/rear winch/quick connects. If you look at your loader section it has a detent on the lower end to place it in the float position which the other valves do not have. If the machine had the valve for a rear mounted backhoe on it that would have the detent also in the lower end. Some of the lands on the spools are different and are fit to each section for leakage and spool clearance so it does not stick or bind. The shuttle ball and o rings in the rear facing the seat, back of valve section should be screwed out and replaced, also on the bottom of each section there is a screw in shuttle valve with o rings that can be changed out. You should have a fitting on the pump tube going into the valve that a pressure gauge can be hooked up to, loader lift at full height, 2000 rpm should be 2450-2600 psi for checking the main relief. You have to have a hand pump to set the reliefs on the a and b ports. Loader lift b port is 3000-3100 psi, loader bucket a port1400-1500 psi, loader bucket b port and all auxiliary valve a and b ports are 2700-2800 psi. So if it was me I would check the centering spring on the bucket valve that it is tight, change the o rings on the shuttle valves, and go from there. There is a lot going on with the inlet outlet sections and regeneration valves and reliefs. I will give it some more thought also.