The factory weld between the upper (rear) tube and the HEGO bung cracked all the way around.
It looks like it was a cold weld, but the wrecks & rolls probably had a lot to do with it, too. My weld isn't outstanding, but I think it'll stick for a few years. I blew through the pipe, but I was able to fill it.
One of these days, I'll replace the mangled HEGO with a new DY-733 (F4UZ-9F472-C).
And I might replace the whole Y-cats assembly (CATCO 9651).