Assuming your leak is from the axle seal, be sure your axle vent is clean and not plugged. As you drive, heating up the rear end, your vent has to breathe, otherwise pressure will build up and push gear oil past the seal. I had that happen to my '51 half ton. The vent was plugged with old hard dirt, grease and paint. After cleaning up the mess on the brakes, I had no further problems and it did not require replacing the seal. I got lucky, maybe you will, too.
The way I found this out was I noticed the leak after going for a drive. I was curious if I had lost a lot of gear oil, so I opened the fill plug on the differential cover while it was warm and when I did, I got a rush of air. There was actually quite a bit of air pressure indicating that the seals were still working. Of course, they are not designed to hold air, so gear oil was pushed past one of the seals.
Kent
