I've got a 2003 A6 4.2L V8 with automatic transmission.

1) Does anyone know for sure what the fluid levels should be in the differentials/final drives on the A6.

I have a Bentley service manual and it states:
Front Drive/Differential - 8mm below fill plug. However I've read in a few forms that you are supposed to fill this so it is over flowing (like transmission).
Center/Transfer Case/Distributor - no recommendation.
Rear Drive/Differential - Over flowing from fill plug (like transmission).

2) As for fluid the Bentley service manual states that the manual transmission and automatic transmission models should use different fluids in the differentials, the manual being Audi part number G 005 000 and the automatic being G 052 145 S2. However it further states that both are SAE 75W-90. Since Audi lists different part numbers I have to assume that one must have a friction modifier additive...the question which one?

 

The automatic transmission fluid is not the same as the differential fluid in the front, center and rear differentials.
You should go to an Audi dealer's parts department and ask what is the difference between the two part numbers, and about which has additives.
I have a 1998 A6 Quattro wagon with 2.8L AFC engine with 2 valves per cylinder and automatic transmission. It has the fill plug for the center differential above the catalyitc converter and above the drive shaft heat shield.
Your Bentley CD is not the same as mine, so you will have to look more closely at your CD, for information regarding the center differential and the drive shaft.
Also, the SAE 75W-90 has to be a synthetic gear oil, such as Mobile 1 or the Audi type your Bentley specifies.
If the seals are leaking, then it is only a matter of time before you go dry. If your car is noisy, then you need to check the center differential fluid level, not just the front and rear differentials.

 

I agree...I was not implying that the tranny uses the same oil as the diffs, just that depending on the tranny the service manual calls out for different fluids in the diffs. I can't see how the diffs on a manual tranny car would be any different from an automatic but this is Audi so.....

I'll contact the dealer and if I learn anything I'll post it back here for reference.

 

My 01 A6 4.2L a/t Quatrro seems to be experiencing some slippage in the tranny. I thought I read that the a/t had a dipstock to check the fluid - true or not? I caanot find one. And what should a fluid and filter change cost? Can a novice handled it?

 

Unfortunately there is no dipstick. The only way to check it is through the fill plug on the pan. If a little ATF runs out of the fill hole between 86F and 113F then you are good.

Although this is for the A8 it should be a good reference for you:
http://www.audipages.com/Tech_Articl...servicing.html

This place sells a complete kit for $115, I didn't buy my stuff here, as I already had a similar fluid pump:
http://www.blauparts.com/proddetail.asp?prod=F2A1004-C

Can a novice handle it? Not sure I'll be doing mine this weekend or next and will post some feedback as to how difficult it was. I see only a few real issues:
1) Measuring tranny temp (for checking after filling). They recommend a VAG-COM which I do not have. I'll have to go by feel.
2) What's going to be in the way of the pan bolts (I haven't looked under there yet).
3) Tools. If you don't have a set of hex sockets you are not going to be servicing much...and there is the odd chance that something under there may be torx.