Modded fill plug for most Axles
 

Ok reason I did this is because the rubber plug is known to leak.
And that's exactly what mine was doing.
First I removed the Differential cover and cleaned it up.
Went to a Auto Parts store and bought a new plug and a nut that it will tighten into.
Then welded the nut over the fill hole and there you have it.
No more leaky rubber plug to worry about.