I changed the ATF yesterday at the S6 and was amazed what came out of it: black, slightly "foamy" and feeling much too little. But now everything is fine again: fresh oil with additive and correct level!
Switching itself is a little softer, but it's much faster and smoother than kickdown! And somehow the car seems quieter.
I used Liqui Moly "Top Tec ATF 1200" and Liqui Moly "ATF Additive".
Same with the Hinterachs-Diff:
black oil. But after 310,000km no special!
One thing I noticed: Can it be that the oil "sediments": I checked the oil when leaving: first black, then dark brown and finally light brown-foamy?! I thought the oil was always rolled over by the gears?
I used Liqui Moly "High-performance transmission oil GL4+ 75W-90".
In this sense: happy change
Sebastian