be very careful removing that bolt, it breaks easy.  It leaves the
non-threaded portion in place that actualy retains the cross shaft
pin, about two and half inches long extendeing through the cross shaft
pin and into the other side of the carrier housing.  for some reason
the manufacturer felt the need to use a lock tight solution on the the
pin.  I usually heat the carrier housing and the end of the cross
shaft pin before trying to remove the bolt.  If the bolt breaks use a
6 inch two arm gear puller and press the cross shaft pin out.The
direction you push is important, push it from the bolt side. You will
have to tighten the press and smack it with a hammer and repaet untill
the retain bolts remains snap. If you press it the wrong way you will
break a chunk out of carrier housing where the pin goes into it to the
left of the cross shaft pin.  The bolt goes in from the right side.
sometimes this damages the cross shaft pin, if so replace it, they
dont cost that much, the dealer usually stocks them as does any shop
that does axle work, ie over hauls diffs. If the press method makes
you nervous and you have access to a dremel, you can grind the end of
the cross shaft pin freeing it from the retaining bolt and then just
push it out enough to remove the remains of the retaining bolt with a
pair of needle nose pliers.  But this means you really have to clean
the diff out really good of any metal shavings from the grinding
operation
also examine the axle shafts  closely when you pull them in the
bearing area. Any sign of burling, burning, or pitting replace the
shafts and the outer axle bearings.  Do not use the axle saver
bearings available that move where the bearing rides on the axle
shaft. The rollers bearings are smaller and it never ever lasts ever.
And yes by all means replace both seals, they are cheap.Pack the
bearing cavity and bearings with a good high quality grease, and the
areas between the bearing and the seal, it will take a while for gear
lube to migrate down the axle tubes. Lube the axle shaft bearing and
seal area as well.  Also make sure the axle vent is free, pressure
build up can blow the axle seals as well. Make sure you use the
correct lube for the axle when you fill it.
If there is one area ford used to really do better than GM light
trucks it was the old design of a bearing pressed on the axle shaft
Ford used to use. This new design that ford uses is the same as GM and
dodge and its weak in my opinion.

Whitelightning