Hey everyone, hope to get a little advice. I am a very experienced mechanic, but new to pwc's. 2006 STX-15F with about 100 hours on it. To my knowledge never been in salt water. Had a small leak when leaving it in the water overnight. Found the leak, coming from the blue coupler area. I'm thinking no biggie, a $14 part. Tore it apart today and found the tiny hole, it was in the bottom of the waterbox. Now I have a few questions. See the pics below the questions.

1. Why would this continually leak water? Since the exhaust tubing loops above the waterline between the two mufflers, I would think that it would leak until it drained the waterbox then stop. Was it just continually pulling water through the engine as it sat overnight?

2. There is a good bit of corrosion on top of the exhaust manifold pipe. I'm assuming that the best thing to do is just replace this piece while I am in there right?

3. Can the pin hole and the seam around it be welded by a good aluminum welder or is it best to just replace it? Those things are expensive, is there a good alternative to the $700 factory part? I'm not afraid to spend the money if it is necessary, but if there is a good alternative I'm open to suggestions.