Look for a set screw in the side of the barrel about a 1/2" or a little more from the rod end of the cylinder. Remove it, and using a soft punch or drift, drive the gland down into the barrel an inch or two. Remove the internal retaining ring from the I.D. of the barrel. Using the rod and piston like a slide hammer, remove the gland, rod and piston from the barrel all together. Before you start any of this, clean up all the dirt, oil and garbage from the exterior of that cylinder. If you are going to accomplish successful repairs, you need to learn how to be clean. You can't fix cylinders with that much crap hanging off them and expect them not to leak when you get done.