Ooh!ooh! A flicker in the darkness!

I've been looking for a while and there's definitely not a whole lot out there about these. I found a data tidbit today, 450 US-1 hulls built compared to 150,000+ Lasers. Good grief.

I have one that I bought as a repair project, (transom is rotted out.) It's been in the weeds for a couple years and I've finally gotten around to working on it. This is my first foray in to fiberglass repairs. Hasn't been too bad so far.
Question you may be able to answer; I'm seeing what looks like stress cracks on the outside of the hull below where the mast step is. Have you seen any of that? Any thoughts? If I have to go digging, now would be the time while the grinder is still close at hand...