I used an old trick when I removed the tank heater nipple from daBenz and installed the plug from the parts car: with the engine stone cold, heat the plug with a propane torch. The plug heats up, expands and breaks the corrosion in the threads. Let things cool off and pulled the plug with a 1/2in breaker bar. Just remember to cover the starter. I used tin foil and shaped it to act as a sluice into a clean oil pan. Well... those were the plugs I was dealing with - right rear.

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daBenz - 1970 220D