Did you remove the grease seal plugs when you greased the wheel bearings?  If not, there is no place for the excess grease to go but through the seal and into the brake drums area. 1/4 inch plug on top of axil, behind brake baking plate.

Mac,
This may be easier than you think....except for pulling the brake drum.

-Pull the drum.
-Disconnect the brake line.
-Unbolt the 6 backing plate bolts.
-Pull the entire backing plate and brake assembly.  (The outer seal and grease cup will stay in position if a sealant was used during assembly)

-You will now be at the bearing retainer plate. (about 1/8" thick and a smaller inside diameter than the shimms)
-Shims are next

This is what you'll see...


The inner reddish thing is the bearing.  The larger diameter thing around it is the bearing cup. (There may be different terminology in the manual.)  It holds the bearing in place.  These are both pressed in.  I've found out that you can remove these by hitting the axle from the other side of the Jeep.  It may not be the right way, but it does work. Use a block of wood.  You may not need to remove these to fix your problem. If they look good, leave them alone.

If you are leaking from behind the backing plate, you should add a small amount of Permatex # 2 sealant to every surface.  Clean up all surfaces on axle, shims, bearing retainer plate, and brake backing plate.  Apply a very thin coat of Perm2 to end of axle housing flange.  Install first shim.  More Perm2. Next shim.  More Perm2. etc... every surface until you get the backing plate re-installed.  Again, very thin coats. 

If you find the leak is on the front face of your backing plate.  This may be your problem....

 
This is, of course, the outer seal.  If yours is old, replace it.  It should be installed with a gasket in behind, and a gasket in front, just under the grease cup. I use a bit of Perm2 on each of these surfaces also.

This approach has worked for me on 2 different rear axles.  Never a leak of diff oil or grease.  Hopefully this helps.

Tim