Sorry, I thought you meant the corrosion was visible and started from a crack that was also visible. I've had one break before I knew what to look for.

I agree, if it's corroded inside the hull material (and not showing on the exposed portion of the fitting), you're not going to avoid that without routine disassembly, which most folks would never do.

There are often (not always) warning signs: rust stains on the fiberglass near the fittings is usually obvious.

Mike