You have to lift the entire cover off the rear axle: It is a two man job, or a hoist job. The cover is very heavy, the lift cylinder and all the control rods of the Zetormatic system extend below it: You have to lift it vertical to not damage the rods, you cannot pull it towards you when standing behind the tractor.
Once its upside down on the workbench, its pretty simple, the lift cylinder is attached by two bolts, and one oil line. If you undo those, you can push out the piston and change the seals.
You can push out the piston by applying air pressure to the port on the cylinder: put the blasting nozzle over the hole and use two fingers to seal the opening, and use short blasts (most air will leak away) this way you dont build up pressure and speed so the piston shoots away from the cylinder. When the piston is coming out, it will loose speed as soon as you take your hands and the air gun of the opening (do not use a screwed connection, this will make it pop like a cannonball !!)