ABS Control Unit - Which is the correct part #?
 

The original part only lists the Bosch Part Number 0 273 004 284, but that doesn't come up on the computer. Instead, it lists all the following part numbers for an "S4 Q Twin Turbo V6 00-02"

0 265 202 403 (ABS Control Unit)

1 273 004 284 (ABS Control Unit)

8E0 614 111E (ABS Control Unit)

8E0 998 375 (ABS Control Unit Repair Kit)

I have a 2000 S4 with Steel uprights.

there should be a letter at the end of all of the numbers... there are a bunch of different ones so
 

be sure... although i think the last one 375 is correct, you just need to make sure the letter at teh end is the same.

Update - Original ABS Unit is 8E0 614 111A
 

The Audi part # for the ABS control unit (aka repair kit) is 8E0 998 375.