[s-cars] driveshaft compatibility

[Chris Coulter]

I've got a 95.5 S6 and lost the support bearing.  I got an A6 replacement
shaft and ended up shearing the rear CV joint apart in about 2000 miles.
Same thing happened on the next one.  Turns out my engine and tranny were
about 1/2 inch too far back.  Moved them up and now I've been fine for
18,000 miles.  I don't know if this was something specific  to my car or a
difference in the A6/S6 driveshafts.