While the "Seal Issue" may be valid, consider the two largest causes of leakage from differentials.
Overfilling
Lack of Venting
When checking the differential for fill, the vehicle should be on a LEVEL surface. The fluid should be just below the fill port, not flowing out.
The vent should be checked frequently to make sure it is not glued shut from mud and road dirt. (Personally, I am changing mine to a vent tube that will be routed up alongside the bed)
Overfilling
Lack of Venting
When checking the differential for fill, the vehicle should be on a LEVEL surface. The fluid should be just below the fill port, not flowing out.
The vent should be checked frequently to make sure it is not glued shut from mud and road dirt. (Personally, I am changing mine to a vent tube that will be routed up alongside the bed)