I have been looking for an early 2000's S4 or A6 with the 2.7L twin turbo. I have read the auto trans are weaker and see a few listed with bad trans but I am curious how does the rest of the drivetrain (AWD) hold up to the power? How strong are the diffs, u joints and other parts of the system that puts the power to all 4 tires? Are there any parts that are weak or problematic? I see a few listed that said replaced control arms are those also a common component that also fails?