Back in 1978 I bought a new K5 Blazer and had it Ziebarted immediately because Blazers were notorious rust buckets. After about 6 years, the only rust was on the bumpers, even though they were coated on the backsides, and the metal part of the roof(!). It seems Chevy painted that with a new material that wasn't supposed to require primer. Hah! GM did cover the repainting, but I've never looked at buying another GM product since.