Squeak came back after 1 month of protectant application. But it was not as bad as before. I often heard some squeak when the wiper turns direction, and this squeak was not consisntant: it seemed to depend on the rain. When the car is driving at some speed, I do not hear squeak at all.

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.