First check the hyd pressure to the pto pack, this should be 175 PSI. do this by putting a guage on either of the pipes that lead into the back ot the tractor, on the right side just above the drawbar, it doesnt matter which, one has pressure and the other doesn't depending on the PTO lever position.
If this pressure is OK then you have a problem with the pTO pack, this is attached to the ring of bolts around the pto shaft, undo these after you have dropped the hitch, and slide the pack out, it's quite heavy. there are 3 big O rings around it, examine these first. if they are ok them put the shaft in a vice and remove the big Circlip from the inside other end of the pack, the plates and eventually the piston can be removed, carefully examine the big cuff seal on the piston and the whole piston. if these are ok then you will need a press to push out the front shaft from the front bearing and cover, on it are 2 "piston rings" , if either of these are broken then thats your problem, replace , with new seals as well, and your problem should be solved. Its not difficult and can be done in a couple of hours. If the pressure is down you either have a pump problem, which requires splitting the tractor, or a fault with the control valve/relief valve, which is under the gearbox top .
