Yes, that's what happened to me too. The head of the bolt is what turned off and there was enough bolt left to grind flats so I could get a wrench on it. The grinding vibration along with PB Blaster broke it loose enough to get it out.

Definitely a place for anti-seize!

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles