Let me know if you find out any thing more about your problem because I had to also have work done on my rear axle.
When my tires were replaced recently, they found oil leaking from the axle on to the left rear brake shoes. I thought that was strange since the dealer had replaced the whole rear end 20,000 miles ago because of a leak that they had found. When I brought it in to the dealer this tiome, they gave me a little bit of a hard time and tried to tell me they would only pay for $300.00 worth of any costs. I did remind them that I have 60,000 mile drive train coverage and they replaced the seal and brake shoes the next day.
Oh, they told me that my 18 inch rims are what caused this problem and it will probably happen again in 15 - 20,000 miles if I keep those rims on my truck. That sounds like a bunch of crap but i'm still looking around to see if I can find others with this same problem.