Verify oil level is at the BOTTOM of the threads.
Sometimes overfilling of the shaft will make lube pass the pinion seal and overfill the rear drive. Keep topping up the shaft, more transfer to the rear drive.
Go at the seal surface with some 400 grit. Get a pristine matte surface. Same for the fill plug surface that mates with the seal. You can even do the same to the seal itself.
Lube is designed to flow into areas smaller than you can see with the eye. Amazing what can been seen with a 10X hand glass that is invisible to the eye. One of the top 10 tools in my bag of tricks.