replacing the seals is pretty easy. It is a little involved.
you will need to take the axle out of that side.
there are 4 bolts that hold the brake backing plate to the axle flange. you don't have to take apart the drum brakes setup but it does help if you do.....
jack up the car in such a way that the side you are working on is raised compared to the other 3 wheels, this is to keep diff fluid from pouring out.( no worries if it does you can refill it with the plug on the drivers side near the yoke.)
other wise prepare a way to hang the drum brake like a wire hanger or something to hold it. release the 4 main bolts on the backing plate then the axle can come out with its holding plate, the drum brake will have no support now so you need to hold it up somehow so the brake line doesn't get damaged. try to move the brake away from the axle because the seal is right inside the axle tube and the brake will get in the way.
slide the axle out you may need a sliding hammer to pop it loose or tap it with a rubber mallet to get it out. a good trick is you install the drum brake cover backwards on the axle hub and put 2 nuts back on for the wheel, then use the drum brake as a slide hammer on the axle hub studs.
with the axle out inspect the shaft. if you find a gouge where the seal sits, start thinking about axle replacement.
inspect the axle shaft splines that go into the diff, look for damage, if the splines are deformed, new axle.
so the axle shaft looks ok, replace the seal. take note of how the seal sits and its direction of installation, take a big flat head screw driver and pry the old seal out, careful do not damage the axle housing. it will be stubborn but come out. take any notes about part numbers that are on the ring, there are different ID and OD numbers on the seals, you need to match it.
get new seal and install it with a seal installer or something large enough to sit on the ring of the seal that you can hammer on and not damage the seal.
carefully knock the seal into place making sure its straight.... now if you find a light gouge on the axle shaft you can sort of control how deep the seal sits inside the axle housing so if you leave it a little out of being fully seated then it may plug a small leak.
some guys coat the outside of the seal with sealer to get more of a seal with the axle housing if there is a problem, the seal has a coating on it that is red and it acts like a sealant when you pound the new seal in, i didn't use any sealer when i did mine.
once the seal is in. take your finger and get some diff oil and spread it on the seal, put some diff fluid on the axle shaft. Don't forget to change the flange Seal also. there is a shaped flat seal that goes to the backing plate.
Now carefully install the axle shaft back in. make sure the drum brake is lined up. Carefully keep the axle shaft centered in the seal as the axle goes in. do not drop the axle on to the seal hard it can damage the spring that is part of the seal, just be careful it has a tolerance you don't want to upset. so keep the axle centered and get it into the diff and make sure it seats 100% holding the axle up and straight start installing the bolts get all 4 bolts in and then torque to spec (i have to look up the torque specs in the manual i can't remember them off hand)
once everything is together you can check the diff fluid level. level the car out on the jack stands, and open the fill plug on the drivers side of the rear pumpkin. you want the fluid to be just at the bottom of the fill plug hole.
if its low you can put some diff oil in.
also now is the time to inspect the axle air vent. on the drivers side by the brake block on the axle is a fitting with a rubber hose that goes up into the chassis rail.
pull it out and change the hose to a new one, inspect the old one for clogs, spiders love to clog up the air vent and you need it to stop pressure build up inside the axle housing.
inspect the fitting on the axle as well, make sure its not clogged. you can take a new hose and blow through it attached to the fitting to make sure its moving air.
then just tuck the hose back up into the chassis rail like the old one was. A bad air vent on the rear axle can cause leaks due to pressure build up.
