A thumb size burr grinder was used to remove the fiberglass exposing an aluminum rivet. The rivet is used to hold the fiberglass panel to the steel door frame. It exhibited light oxidation but otherwise looked fine and the surrounding fiberglass looked fine as well. Oxidation must have been the culprit.
It would have been easy to fill the hole and sand the other areas smooth. I decided to grind out the other areas and remove the rivets instead.
New aluminum rivets were installed then buried in several layers of fiberglass matt and resin. Green masking tape was used to channel the excess resin off the door.
Remember, our fiberglass is clear. The rivet heads you see are buried deep, sandwiched in matting and are not exposed to air. Chances of these rivets oxidizing are sip, zero, nada.
After the fiberglass set up the masking tape was removed.
30 minutes of grinding and sanding produced a very nice repair job. We will shoot this with primer when the rest of the door is ready for it's second coat. The drivers side door is fine. There are no other similar repairs needed.