i had the same problem with the axle fluid leaking into the drum, but i didnt have the same bad luck as you. i replaced the inner seal myself, the outer seal had to be changed at the dealership because of the need for a puller. if you have ABS they get you every time with that too because apparently the little gear before the outer seal has to be cut off and replaced with a new one, it cant simply be pulled off. if you have your truck worked on at a dealership and it didnt get fixed, i would take it back to them and say you paid to have it fixed, and its not fixed. somebody at that dealership needs to fix your leak even if it means getting you a new rear axle. see what they have to say about that
good luck with the leak tho hope you can get them to fix it for no more cost to you