5243 hydraulics won't lower

Just bought from an estate a 5243 with low hours. Sweet running machine, but apparently not used for some months (years?). Three-point hydraulics lift up when hydraulics are energized, but won't go down. The up motion happens no matter where the implement control lever is positioned, even in the down position. I suspect an internal valve is stuck or rusted in the up position. Any ideas?

are the arms trying to rise all the time , in which case it could be a stuck valve and the releif valve would be blowing constantly

or are the arms just not dropping... its only their own weight that makes them go down ,if the crossshaft is stiff they aint heavy enough , try standing on them with the control lever in the lower position