I think it just rusted through but did not look any different than when I bought the boat four years ago. The stub could be a real issue since it broke off almost flush with the surface of the exhaust coupling. I have a replacement nipple and we are not going anywhere until the end of cyclone season so Aprilisih. I think I might have a go at it in the next couple of weeks and then I can take it back to Canada when I go for Christmas. At least the machine shops there will be familiar with the thread - they use metric or some British standard thread here.
Heading back to Lake Ontario for this summer. Now in Bermuda and heading to Long Island Sound in the first week in May. Then on to the Hudson and the Erie Canal.