Today went to a shop that does tranny rebuilds:
upon draining the Castrol GL -4+ with VW specs they found metal debris in it.
So that 1-2 month stunt I did with GL-5 in the transmission of my A4 was not without consequences. I'm planning to have them tear down the tranny in a few weeks and do the rebuild.
What pisses me off is that the shop where I ordered the transmission oil change did not utter a thing when I gave them GL-5 to pour into the rear diff (correct) and the tranny (grossly incorrect)
I wonder if they should pry open the torsen to inspect (130k miles on the car) while they are at it or the clutch plates wear check (suggested by JB) is the only thing to watch out for.
While checking the tranny they found a busted ball joint. This is a lot like going to a dentist :-[