Remove the jack bolts then remove the clamp plate .
Pull the shaft  out of the receiver housing . The clamp springs  may fall out of their location.
Remove the lock nut  and piston  from the shaft.
Replace the o-ring  and quad-ring  on the piston.
Replace the quad-ring  and o-ring  in the receiver housing.
Lube all o-rings and quad-rings with hydraulic oil.
Install the piston  on the shaft . Tighten the locknut  to 100 ft-lbs.
Note: You can install the clamp plate  on the shaft and hold the assembly by the clamp plate in a vise to loosen/tighten the lock nut.
Support the shaft vertically. Install the clamp springs on the piston. Lower the receiver housing onto the shaft. Install the clamp plate and use the jack bolts to raise the clamp plate until the piston is fully seated into the housing.