Are you saying the hitch is still raising normally in LD position and is lowering too slowly? Are other hydraulic functions working normally? Usually the rockshaft loses ability to lift in L position when linkage is worn or out of adjustment. Losing function in D is unusual. If leak at load control shaft and raising/lowering problems started at same time, you could have a broken load control shaft. There is a bushing that has an oring in it that helps the control shaft seal to last longer. The other things that help is to replace the shaft if has any wear and also replace the bushings and front pin in drawbar support. Then be sure to shim the drawbar support so it has no side to side play. You also could have problems in the control valve or internal linkage. I would repair the leak at Load control shaft to be sure shaft is ok. Also look in bore of transmission case when shaft is removed to be sure the fork that straddles shaft is not broken.