Assuming you are talking about the mixing elbow
, the ones I've seen fail have started slowly leaking through a crack or corrosion
pocket externally. Normally somewhere close to where the exhaust gasses and the water
I guess some of the fancy ones could fail internally first, and the indications would be subtle, maybe hissing as the leaking salt water
turns to steam on shutdown?
I've patched a few to get home, or put up with the leak, and slight exhaust smell. But it was not a sudden catastrophic failure. Maybe the more modern fancy ones might be different?