I believe he's talking about the bolt at the center of the top of the air filter housing cover.

One of my cars had the same thing happen. The metal seems to be pretty weak as if they just threaded a casting - it doesn't seem to be hardened at all.

I haven't done anything on mine and just use the four clips. But it bothers me because I worry that dirty air may be slipping by the rubber gasket on the air filter. No evidence that is happening by looking inside, but if I could fix it somehow I'd be happier.

Ken300D

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