Wd 3-point hydraulics

Assuming that isn't the problem and that the hold postion valve is working correctly (quick check, raise lift to max, put in hold postion and shut down tractor, with *no* weight on arms loosen but don't remove hold postion valve from top of pump, lowering control should drop lift arms {may have to stand on arms} with oil "leaking" out from under hold postion valve {you may want a bucket under pump to catch oil}), the only other valve involved is internal to the pump.

With the control dropped past the hold postion a by-pass gallery is opened in the pump allowing oil in the ram system to drain back into the reservoir. It is possible that some crud is blocking this gallery especially if the hold position valve was off the top of the pump for a while (which may not be what you meant by "disconnected", I don't know). You'll have to pull the pump (a learning experience to be sure) in order to clear this passage.

I'd check those first items before pulling the pump.