Tractor Repair: 1964 FORD 2000 HYDRALIC CONTROL, piston seal, water infiltration

Question
THE 3PT HITCH ON MY TRACTOR DOES NOT LIFT UNLESS I PUSH DOWN ON THE DRAFT CONTROL LEVER. THEN IT USUALLY LIFTS, BUT IT DOES NOT MAINTAIN HEIGHT. NOTHING LEAKS, AND OIL DOES NOT LOOK LIKE IT IS FOAMING, SO I DO NOT SUSPECT WATER INFILTRATION. I HAVE BEEN TOLD THIS CAN BE FIXED WITH AN ADJUSTMENT, BUT I WOULD LIKE ADVICE BEFORE I START TO TAKE IT APART.

Answer
Hello,

  You may not see any oil leaking on the outside, but there may be some leaking on the inside.

  Check if it will stay in the raised position after shutting off the engine.  If it settles a small amount in an hour or so, that's OK, but if it goes right down then the piston seal in the lift cylinder may have an internal leak.  If the seal is OK, then the hitch control valve should be checked for a sticking spool or a check valve that is not seating.