I found an easier way to fill/add gear oil.
On the passenger side axle tube, there is a ventcap that can be removed with a 15mm wrench.
I take that cap off , then thread the plastic tube from my 6 dollar "outboard gear oil" pump into the hole and fill that way.
Less messy than filling through the axle fill plug (located on the driver's side of the diff, facing the front of the car). I always find that the axle damper (dogbone) is in my way (though the dogbone is easy to remove)
I think I found the vent cap trick on this site - you may want to do a search.