Not only did I leak test before putting it into a computer, but I had leak tested it for years when it was in my van! (I removed the heatcore and blower before I sent my dead van to junkyard last spring.)
I don't know why that join split, and that bothers me. There would have been some stress on the inlet/outlet from the weight of the hoses, but that shouldn't have been significant. The core was held in place by a strips of wood screwed to each side, then bolted to the top of the case. Shouldn't have been any stress from the mounting. The whole system is brass and copper, no signs of corrosion anywhere.
