Need some advise. I was going to drain off some coolant to put in a new t stat in my recently acquired 1981 240D. But the radiator plug doesn't want to come out, it just rotates. It's been a few years since I had my 300D's plug out. Isn't it plastic with threads that go into the rubber grommet ? Can I pry slightly under the head while I turn the plug to get it to start out? FYI, the plug isn't leaking.

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David McDonald
1981 240D
1985 300D (wrecked)
1985 300TD 365,000 miles
1969 Mustang Fastback