One thing that tends to get overlooked is to check the vent to see if its plugged or not before replacing the seal, when I used to work at the Dodge garage out of high school if a vehicle came with some a pinion or axle seal leak we always checked the vent to see if it was plugged and alot of times it was, if it can't vent the air when the axle warms up it will start pushing air and fluid out of the seals.