I tried mother's, did work. I will give Turtle's a chance, but this smut is REALLY thick and feels smooth like it has become integrated into the chrome.

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04 X3 2.5i (Retired)
04 X5 3.0i (Retired)
06 X5 3.0i (Retired)
07 X5 4.8i (Delivered 6/20/07)