A4 manual transaxle/rear diff fluids?

["mstocker" <mstocker@neo.rr.com>]

I called my local Audi dealer today to see what fluids are
used in 1996 A4 Quattro's manual transaxle and rear
differential.

They stated:
  * Manual transaxle: 75W90 synthetic gear lube
  * Rear diff: 75W90 conventional gear lube

Is there a reason why the difference in lubes?  Is there a
reason not to use synthetic in the rear diff?

Thanks.

Michael Stocker  <mstocker@neo.rr.com>
  1989 90 Quattro    1996 A4 Quattro