I owned an '85 5000S. It was good until around 120K. Then it started falling apart. I finally got rid of it with 190K on it. The last 50K mile probably cost $10-$12K. Fortunately, I purchased a five year UNLIMITED MILEAGE warranty, so the insurance co. took the bite for most of the cost.
The weird thing is, I loved that car. The interior was so plush compared to a 300D of the same year. I think the Audi retailed for around $20K and a Mercedes around $32K. Although when you factor in all the $$$ spent on repairs, the Benz was still a better deal.
I have always liked the way Audi's looked and drove. The big draw back is resale value, they have had a history of poor resale. Audi still hasn't recovered from the hatchet job 60 Minutes did on them.
I'd own one again, except I've had such good luck with Mercedes.
91 300E 120K
90 300SE 275K (sold)
92 BMW 525iM 120K
90 BMW 525iA 175K
85 300D 175K (sold)
84 300SD 245K (sold)