Removing the Endcap and Piston

Before you remove the endcap, drain the oil from the wrench.

Position the oil ports over a suitable container.
Pull the piston rod out until it stops.
Push the piston rod back.
The oil from the tool runs out through the ports.
Put the housing in a suitable vice to hold it safely.
Remove the endcap with the tools listed and a suitable hand torque wrench or breaker bar.
It can take considerable force to break loose the endcap threads. Apply axial force to the endcap tool to keep it engaged while breaking loose the threads.
Fully unscrew the threads and pull the end cap and piston assembly from the wrench housing.