Same happened on my 2018 C7 Grand Sport!My 2014 C7 has about 11,000 miles on it and is seldom out in wet weather. In spite of that, I just discovered that the nut that holds the left hand (door side) driver's seat track in place is severely corroded (see pic 1) The stud seems to be fine (i.e., rust free). The right side (see pic 2) and both of the passenger side nuts and studs also look fine.
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It seems likely to me that GM may have gotten a bad batch of nuts. My dealer tells me he is not aware of any bulletin about a problem, and that he sees almost no demand for replacements.
Has anyone experienced or are aware of a problem with seat attachment mounting nuts rusting or is this a one of a kind occurrence??