May be it's because of the white color; it absorbs less heat from the sun, more humidity around the panels.?

I had a white 4Runner 12 years ago, it was always rustproofed every year since new, and even then, rust was forming under the wheel arch mouldings and rear tail gate. I didn't have those problems with a black Toyota pick-up and other darker cars.

Would be interresting to hear from other white X5 in the rust belt.

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