Replacing a "rear propshaft" seal

After doing a complete timing belt job recently, I thought I'd take it easy and tackle something a bit less involved: replacing the leaking oil seal between the center differential and driveshaft on my 2004 Audi allroad.

Once again, my Quickjacks were invaluable for this project. This is a job that I used to take to a shop and pay lots of money for, but now I can easily do it myself.

The job involved: (1) disconnecting the exhaust pipes at the middle of the car to allow the catalytic converters located under the center differential to drop down; (2) removing a few heat shields; (3) disconnecting the driveshaft providing traction to the rear wheels from the center differential flange; (4) removing the aforementioned flange; (5) peeling out the leaking seal; and (6) installing a new seal and putting everything back together again.

Unfortunately, I stripped the head of the bolt holding the flange to the center differential while trying to remove it. This meant having to spend A LOT of time drilling out the bolt head (which I could not get out with a stripped bolt extractor because the bolt metal was so hard). In the process of destroying the bolt head to free the flange, I also had to damage the surrounding area of the flange, so that meant having to source a replacement flange.

The vexatious bolt, after I destroyed its head.

The innermost concave area of the center differential flange where the bolt head sits was slightly damaged after my extraction efforts.

Fortunately, I was able to find a cheap used replacement part in very good condition from a fellow Quattroworld user.

Here is the replacement seal, which had to be pounded into the differential with a large 1 1/2" diameter socket (not shown):

I had stripped the head of the bolt holding the flange to the center differential while removing it because I had trouble holding the flange still while trying to wrench off the bolt. When reinstalling, I came up with this rather ingenious way of securing the flange in place: by slipping a coupling washer over two of the long bolts used to connect the flange to the driveshaft, screwing one of those bolts into one of the holes on the side for the center differential heat shield bolts (which were removed), and screwing the other bolt into the flange:

After that, the reinstallation was easy-peasey.

Here, the flange gasket is in place and grease for the driveshaft CV joint has been packed into the flange:

Here, the driveshaft and center differential heat shield are back in place:

And here everything is back together again. I got a pair of shiny new replacement exhaust clamps as part of the kit I bought from Blauparts for this job:

I figure I saved about $700 or more doing this job myself, but, as always, the wrenching experience I gained and adding to my car repair repertoire were far more valuable to me.