I had the same thing on my 92 300e. About a month ago I made a tiny hole in the top of the rubber boot on the ball joint and injected some 30 weight oil with a plastic syringe. Immediately stopped the noxious creek. This weekend I am replacing the ball joints, but only out of "preventative maintenace" (is hasn't creeked at all since getting lubed).

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89 300te 222,222
92 300e 190,000