The seat valve has a spool valve that controls the seat base position by oil flow to an attached one way cylinder. The cylinder oil is also tied to the accumulator that cushions the cylinder piston to provide the ride. The cylinder has a leak off line that lets seepage oil return to the transmission case. The seat valve contains a pressure reducing valve and the position spool, that have o-rings that need replacing due to age. You can remove the black plastic panel below the seat and check out the linkage to be sure its functional but a seat valve removal and overhaul is most likely the fix. There a special tool needed to pull the pressure reducing valve out of the housing. Hope this helps.