Thanks for the input. Probably sloshing water in big seas finished them off. The port tank always oil canned and made dramatic thunderous sounds even in calm weather when you turned on the tap. Yes, you can reach all the welds from the access port by hand.

I assume the other three baffles ( one in the port tank, two in the starboard) were constructed the same way, so the construction design only has a 25% failure rate. Could be the welds in the other tank were just better.

-Kafl