I'm looking at purchasing a used Audi A6. There are a few 2004 3.0s for sale that I have looked at. Specifically, there is one that has under 13K miles. I ran a Carfax and no alerts were shown. What are some known areas of trouble? I also looked at an '04 S-line. It was a little above what I wanted to pay. Also, saw a 4.2; however, it was gone in 2 days.