If it is like the ones on a 4400 and I think it is.
Take the cylinder off the combine and put it into a vise. Remove the hyd fitting from the butt end. Extend the ram until you see the end of it in the hyd port. Working through the hyd port with a small screwdriver, work the snap ring off the ram. Pull the ram and replace the packing. Reverse to reassemble. The hardest part is working the snap ring back on the ram through the hyd port.