Tractor Repair: IH 574 3 point hitch, lift, stuck

Question
When the tractor is started the three point hitch will go all the way up and won't drop down. The 3 point will "leak" to its lowest point in about 24 hours when the tractor is not running. When it is started again, it rises back up; it will lift the bush hog.  The steering, brakes and loader all work fine. The fluid shows full on the dipstick, I have changed the hydraulic filter.

With the bush hog on the tractor I can move the drift lever to the full rear position and it might drop an inch, there is no consistency but the movement usually occurs at the top position.  Moving the position control or the rise response lever to the forward or rear position has no effect on anything.

Any help would be much appreciated. Thanks,

Answer
it sounds like the linkage controlling the lift spool is after coming off internally have you noticed any difference in the stiffness of the lift lever,is it easier or harder to move.Have a look at the lever linkage externally but most likely its internal and you may have to take off the top cover to find the fault