I fix these all the time. The steel nut cages and the steel nuts are in a hostile environment and are prone to corrode because of the dis-similar metals (aluminum hood and steel nuts and cages). Once the nuts start spinning, the fun begins. if you ever have the hood off, run a metric tap in all the holes to clean up the threads of the captive nuts. Also use plenty of anti-seize on the bolts during re-assembly.
I am sure there are many less sophisticated fixes. I cut the flat nut cage area off the hood frame, rebuild or re-make the nut cages, restore the nuts, aluminum butt-weld the repaired section back in place. The welds are ground smooth. When done right, the repair is undetectable, with no fillers or exposed welds. Takes me about two hours per side on badly damaged ones. No paint damage on the exterior of the hood when done properly.
The quick and easy fix, is to just hole saw a hole in the hood frame and hold a new nut in place.