Yep, they use acid on the roads here in Maine. The inspection station guys are shocked at the condition of my X5 after ten years and almost 200k miles. Weekly underbody washes and Krown undercoating are the key.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim