Anyone have a method of getting a differential fill plug out after its been stripped pretty bad??

 

Were you using a torque wrench, when this happened? The fill plug is taken out so often, that the specified torque may be too high for worn threads.
Which year A6 and which engine and transmission?
I am not sure as to how to do this without removing the whole rear differential to drill and retap the hole for a new oversize plug or getting a used differential part with a good refill hole and plug. You will have to read your BentleyPublishers.com Audi shop manual CD.
You will need a transmission jack to remove the rear differential, which has adjustable tilt.

 

its a 2000 a6 avant 2.8L...a 10mm allen head is what fits in the plug. I was trying to check the diff oil level for the first time since i've owned it, and i think since there was rust and crap in the hex head i didnt' get the wrench in all the way and it twisted, stripping the head when i tried to loosen it.

 

The rear differential plug on my 1998 A6 wagon with an automatic and C4 chassis uses a 17mm allen wrench.
Since you didn't strip the treads, you will need to order a new fill plug and somehow get the old one out.

 

There are several ways to remove the plug. First, clean the old one out really, really, really well. Take your allen wrench and seat it in the plug. Take a hammer and pound the wrench even further into the plug. 9 times out of 10 you'll be able to get it out. If this does not work, get the new plug, take the allen wrench and car to a exhaust shop, have them tack weld the allen wrench to the plug, remove the plug, check the fluid and put the new plug in. Be sure to use anti-sieze on the new plug.

Bob

 

Another option is a cold chisel and a hammer. With the chisel, make a cut on the plug and then use the chisel and hammer to turn the plug counter-clockwise... being careful not to damage the casing of the differential.
Obviously a new plug will be required after you refill.

 

Cold chisel and Hammer LOL LOL -- I like Bob Martin's sugestion better - less chance of hurting your fingers --

 

It saved my bacon more than once...!I guess that would explain the end of my piano playing career! LOL

 

i did the same thing with my a6,but its going to be hard to use a hammer becasue theres no room to get a good wack with the hammer

 

I am not sure as to how much space you have on a 2000 A6 Avant rear differential at the fill plug. There are very thin abrasive cut off disks, which may be able to cut a groove in the old plug for a screwdriver. However, this would only work with a flanged plug which extends above the hole. Also, you would have to be careful to not cut into the sealing surface below the flange. Most screw drivers are not wide enough, so you might have to make one to fit.