This is the van's 2nd axle. I replaced the factory axle with an exact donor axle with only 51k on it. It came from a church van that only saw occasional use. When I had it swapped out, I had the axle seals and pinion seals replaced with brand new GM OEM seals. Now pinion seal is leaking (but not the wheel seals). It just recently started leaking - it was not leaking a 4 months ago when I was under the van inspecting everything. Its not dripping yet but I'd like to get ahead of it. I verified that the vent & vent hose is clear from the axle to the end of the hose.

For the last 2 years/10k miles, the van has mostly been sitting - I drive it once or twice a week. I'm baffled as to why the pinion seal is leaking so soon, especially with such light use. So far, the only possibilities I can think of are:
1.) The mechanic didn't actually replace the seal, or used cheap seals and kept the GM OEM ones I gave him. On the invoice he charged me labor for it and I don't have any other reason to distrust him.
2.) The seal had some quality issue (this is more common these days) and has just prematurely failed.
3.) There is something wrong with this axle and it has damaged the new seal (unlikely, only has 61k of light use on it).
4.) The mechanic didn't do something correctly with the removal/install (also unlikely as he also builds custom axles and likely understands backlash/torque/etc., also no noise/vibration.)

The axle makes has no noise, vibration, irregular behavior, or other things that indicate trouble with it. Within the last 2 years/10k miles I also had the u-joints and center bearing replaced (Dana Heavy Duty Spicer Life Series u-joints and GM OEM center bearing) and had the driveshaft stripped and re-balanced. When I got the donor axle I drained it myself and had the mechanic refill it with my own Valvoline synthetic 75W-90 gear oil; I got a sample from the fill plug today and it's still very clean with almost nothing on the magnet.

I just ordered a new pinion seal and I'm going to change it out. I'm going to mark the shaft, yoke, axle and count the turns to make sure everything goes back together the same way. I'm wagering on a faulty $24 seal - if it leaks again it will go to an axle shop to be checked/adjusted. Just not sure what to make of this.

 

Sometimes the new seal sits in a slightly different spot from where the previous one was and ends up riding on some rust causing it to wear quickly. Also possible that the yoke had a groove in it. My '15 with 50k mi has slight evidence of a very slow leak (wet but doesn't drip) and I left it alone when I swapped in a new limited slip differential.