My 2004 A4 manual states that factory fill is 0W-30 and that 5W-30 and 5W-40 are acceptable if the 0W-30 is not available. Specs to meet are ACEA A2 or A3, API SJ.
That has since been superseded by TSBs and a class action for the 1.8T, and a VW 502.00 approval is required on top of the above.
I've used M1 TDT 5W-40, M1 0W-40, and (currently) GC 0W-30. [censored] if I can tell any substantive difference.
dparm, I thought the 2005 S4 manual of yours that you scanned into the other thread said 0W-30?