Rear roof trim worn

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Not sure what it is called, but it is the steel or aluminum trim along the bottom corner of the roofs, in this case , the rear roof. The white coating on mine is wearing away in about a 1 foot section. (see pics).
I have no trouble opening or closing either front or rear roof. All 4 corner aluminum latches are easy to engage.
I have no idea as to why it is abrading and once corrected, is there something to re-coat the trim. Thanks.