Rear diff plugs frozen

[Austin Calise]

Jay, one sure fire way to free them is weld a wheel lug(17mm head) into the drain plug then use a bolt out socket(or appropriate underside 12 point socket) hammered
onto the threaded portion of the wheel bolt, I've done this on the bench. Use appropriate fire protection aka a welding blanket to shield the gas tank if doing on the car. 
The new drain/filler plugs from audi may be different triple square although ECS is showing them looking the same pn#  WHT001937 they also sell a magnetic hex drive plug there too.
The size is M24X1.5 and there are many other options too factory audi to bmw to aftermarket all less prone to stripping out like the factory 17mm allen plugs.

-Austin