Up to where I can see from outside, the front edge of the front fender is covered by white paint.

Where moisture is captured, rust can form, even if there is paint.
E.g., edge of doors, edge of trunk hood, etc.

Some things penetrate paint, though very slowly.

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