For the plug, I would take the car on a freeway run for 15 minutes or so and get everything good and hot. That should improve the chances of getting the old plug out. When you get it out, use a 1/2' 6 point socket from now on and you won't ever have that problem again. 1/2" is 12.7mm and fits the thing perfectly.

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.