hydraulic leveling jack replace / rebuild

I have a used 2002 Allegro Bay 36' Class A I recently bought. The hyd. jacks go down but the right side jacks won't retract. All jacks go down and will level the rig but while trying to retract/store the jacks the right side (F&R) only retract enough to put the tires back on the ground. I have replaced all of the return springs (2 on each jack). What a pain it was to have to dig under the jack enough to use a floor jack to jack the cylinders back up. They jerked up a little a time even with the T fitting bleeder caps loose on each one. Mine are 9,000 lb jacks.

I do most of my own repairs so my question is has anyone ever replaced their jacks or had them rebuilt?
New replacements are around $600 each.