I have a 65 chevelle. Looked like there was some rust on the body under the rear bumper. Looks like they just bondoed over it when they painted it. Looks sloppy. They probably didn't care because it is hidden by the bumper. Are those body pieces replaceable like the ones that are in the front behind the bumper that run under the headlights?

If the place is what I think, then NO it is not made aftermarket. I was able to trace the outline on some paper, transfer to sheet metal and make new ones, then cut our the rust/bondo and weld in. Not overly difficult.