You mean like a split-ring retainer? on the outside of the box? Are you talking about the main oil seal around the output shaft which the pitman arm is attached to? Mine just had the metal re-inforced rubber oil seal holding itself in, I didn't have to remove it from the vehicle to change the...
I can't fully remember what I did when I did mine, but I think I just belted a big screwdriver down next to the shaft which bent the old seal, then I just levered the screwdriver around popping the seal out, this totally buggered the seal, but the end result was what i wanted.