I have the same situation on my '97 E 300 D, which came very rounded off. I also have a new drain plug, but, I have reefed on it as much as I am comfortable with. I am afraid I will end up with no threads in the pan. So about 7 years ago I resorted to sucking the oil out with a Topsider. Now I would not use the drain plug if it worked.

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'97 E 300 D