What's considered excessive oil consumption with the [3.5L] OM603.971?

Any reason for the 3000 mile oil change interval? You can get an analysis done to help you determine how contaminated your oil is at that time. At those prices, I'd be looking to do this

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting