Yesterday while pulling the rr brake I noticed there was a heavy covering of thick oil on the calipers and the surrounding area. I am suspecting it is diff oil, however the diff appeared full. Is it possible I have a leak in the axle seal, and if that is the case, how difficult is it to replace this seal?

 

If your axle seal is leaking, plan on replacing the whole hub, as well as the brake pads if they any grease on them.
Might check out Rover connection for rear hubs, they have both the OEM and after market.