End caps that bind on the rod are NEVER reusable. It's the cap itself that has corroded, not the 'o'rings. Buy a new cap and seal kit before you start the job. Rescrew the end cap and pull the rod and piston out. Remove the screw holding the piston to the rod and then remove the old cap from the rod. Clean up any aluminium from the rod. If there are any deep scratches on the rod, consider replacing it. Fit all new seals in their respective places. With the cleaned old rod or a new rod, push the new cap onto it, put the piston in place on the end of the rod and torque the screw to spec. Fit the assemlby back on the cylinder and screw the end cap back into the cylinder and torque it.
Chris.......