As long as the circlip is still on the differential end of the cv axle, ( looks like a round metal split ring) you just push it back in the diff, making sure it engages the teeth on the inner differential, then give it a good tap with a mallet. Usually this is done with the cv disconnected from the locking hub. You don't need new seals. If the CV is still connected to the front hub, you may not get the swing arm to drop far enough to install the spacer. You may have to disconnect the front locking hub, remove the circlip holding the cv in the hub, and disconnect the strut to allow everything to drop far enough.There may be easier ways to do it, but that's how I did and do mine. Maybe someone else can chime in with an easier method? Also you may need some way to compress the coil far enough to reconnect everything once it's in place, like a come-along wrapped around the a arm and strut tower, or some guys have braced the upper strut tower from the engine compartment to something solid , like the roof of your garage, with a long board, then used a floor jack under the control arm to lift everything back into place.
