Sometimes there's no oil contamination of the coolant. Sometime, like in my present 1990 300SEL, the head gasket leaks oil externally down the side of the engine. I'm told that it's actually very common in 175K mile engines that don't have the "milk shake" condition in their coolant.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio