My M103 has a block heater just behind the drain plug, kinda between and under 5 and 6 Ex. ports. Brass w/orange colored plug cover. See photo. This engine is in a w126, but that shouldn't matter should it. Just asking. I also removed block drain plug this summer with no problem whatsoever. Appears to be original (1988). Let us know if you proceed and how it turned out.

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