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.
Back in the water in Grenada - with new main and #2 and cockpit canvas (Santa came early). Will spend the winter and early spring in the Caribbean and then head to Bermuda and the northeast US. Still trying to decide if we will bring the boat to Canada, either in 2015 or 2016.