This came up a few months back in the diesel section.

My rotors lasted 300,000 miles and the feedback I got is that they could have kept going

http://www.peachparts.com/shopforum/diesel-discussion/355786-my-potentially-300-000-mile-brake-rotors.html

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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."