Ditto what Bruce said. Its called filiform corrosion, and can occur under a clear coat or even under ALclad aluminum plated alloys if the surface coating gets nicked, which are much more vulnerable to corrosion than pure aluminum. You will probably also see it at the corners of the bolt holes on the stock MB wheels, where the edge is fairly sharp, leaving the clearcoat very vulnerable to damage from removing the wheel bolts. Its one reason to like chrome* plated wheels with no sharp edges.[
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*Where "chrome plated" means a copper base layer, followed by a nickle overplate, followed finally by polished chrome.
]*Where "chrome plated" means a copper base layer, followed by a nickle overplate, followed finally by polished chrome.
