I'm looking at a 2003 Audi S8 with 164k miles, for $6.4k. It's a beautiful car, the body and interior in almost great condition, except for a couple minor scratches, normal wear and tear for a car pushing 15 years old. It comes with an extra set of wheels with winter tires, as well as maintenance records all the way back to 2009, all from the Minneapolis Audi dealership.

A couple things I'm a little concerned about are 1) the transmission just got rebuilt. The original owner was going to scrap it, until the current owner bought it and had the tranny overhauled. On the test drive it seemed to drive and shift great, with no noticeable issues.
And 2) the catalytic converter was replaced 4 times since 2009. That is definitely something I don't want to have to deal with almost every other year. What could be the reason for this, and should I be concerned about it?

Is this car a good deal if I can talk him down to an even $6k?
What are some things that I should look at or keep in mind when I look at this car?
What are your personal opinions or experiences with this vehicle or engine?
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I'm also looking into:
2004 S4, 130k miles, $6.5k
2004 Allroad 4.2L, 160k miles, $5k
2003 A6 2.7T, manual, 140k miles, $5k

I had an '05 A4 3.0L manual up until a couple weeks ago when I hit a deer and totaled it going 45mph. I would love any advice on the other Audi's I'm looking at.

 

I bought my 2003 S8 from the same dealer, nearly ten years ago. It's a great car! While I don't have any feedback on the trans, the cat issue can be remedied. My car had 70k miles when I bought it, and it had already had 2 cat converters replaced. I replaced two others prior to 100k, both under warranty. When another went bad, I had an aftermarket Walker cat installed. I'm now at 248k miles w/ the same cat converter.

 

Did you buy it? (the D2 S8) I put 110K on my '03 D2 (had 95K when I bought it). Loved every minute. Mine was MTM-chipped (doesn't do much for non-turbo engine, but did remove speed limiter and would rev to 7400 before cut-off). Transmissions last almost exactly 150K--rebuilt mine for $1500 and it was perfect when I sold it 60K later. Absolutely loved the sound and thrust of that 4.2. Replaced it with a '15 D4 2 years ago. Quite a change... Like parts of the D2 better, but the D4 gets MUCH better gas mileage (true 26 mpg on long trips vs 21m pg with my D2) and OMG the acceleration!