They are rather easy to do as long as you have the pitman arm puller. Remove the pitman arm, remove the large internal snap ring that holds the seal in place, then loosely reinstall the nut and washer (as a retaining device for the seal.) Then start the car for about a 2 seconds. The pressure will blow out the old seal (and most of the fluid if you dont shut the car off quick enough.) Very messy but far easier than completely removing and overhauling the entire box. This is how the regular line mechanics would do it in the old days. Then grease up the new seal, slide it in, tap it the rest of the way with the correct size large socket, reinstall the snap ring and pitman arm and you're done.
