Fibreglass Fenders

[dodj]

I have fibreglass fenders on my Challenger. Back when I swapped a Remington rifle for my car there were no aftermarket fenders available other than fibreglass...so...that's what I got. They continue to serve me well. But recently I have noticed a few 'star' cracks in the paint.
See attached. Is this just something to sand out?  Or is it something going on with the fibreglass?
 

[Marty]

Those star cracks are from rock/debris thrown off the tire and impacting the back of the fiberglass. Common on old Corvettes. You can't sand them out. The resin or gelcoat surface is damaged and must be ground out and re-glassed.