I have done this to several axles including these. Take the driveshaft loose, take the nut loose, replace the seal, and then re-install the nut. No crush sleeve needed.
Getting the nut loose if it's not loose already can be a problem. The best way is with a large impact gun. If you are using a breaker bar, it's difficult to jack the truck up high enough to use the bar, and also hold the truck steady so you can turn the nut. Impact gun is the way to go.
On the crush sleeve thing, the crush sleeve sets the pinion bearing pre-load. The distance between the bearings can vary during production, so the cheap easy way was to use a sleeve that will crush and shrink with a given torque and pre-load or put tension on the bearings. When you get there, the pre-load has already been set, the sleeve has already been crushed to the correct distance. All you are doing is putting it back the way it was. It takes a lot of torque on the nut to crush the sleeve, so you do not need to worry about getting the nut too tight and crushing the sleeve anymore.
These nuts do like to work loose, it was a known problem with these rearends. A little locktight can help it from coming loose again once you get it tight.
