How full do you fill your front, center, and rear diffs? I have seen to fill just below the refill cap, and also i've seen to a set mm distance below the cap. Which is correct?...2000 a6 2.8 automatic by the way.

 

Just until it begins to run out, with the car level.

 

anyone else?..the bentley book says up to 8.5mm below the cap on the front, up to the cap on the rear and doesn't even say on the center. wouldn't normally be that concerned if it was close but it says in the bentley book they are very sensitive to being overfilled...not sure what would happen if you did though.