Lenar 254-2 3 point hitch won't stay up

[Mike Collin]

The three point hitch lift does not have enough power to lift my weight if I stand on the drawbar. It will lift the drawbar with nothing attached, but creeps down when lever is returned to center position. If the aux hydraulic isolation valve is closed (round knob under seat), the drawbar will stay up and I can stand on it without settling.
Could it be some sort of relief valve with gunk in it, or bad o-ring on lift valve?

 

[piper184]

I would suspect an issue with the control valve itself. If it is leaking internally that would explain both the low power in lifting and the creep. The knob under the seat only controls how fast the fluid flows back into the tank. That lets you determine how fast the 3 point lift will drop. If you close it all the way it will prevent the lift from dropping at all.
Do you have a parts book that shows the internal parts of the control valve? Hopefully it is just an o-ring or seal that is leaking and can easily be replaced.