I have a feeling that the hot gases "condense" right at both the cool waterjacket area and where the tight bend is, both in about the same location.

There are several ways to improve this piece... one way would be to make it bigger, for better flow, polish it to remove areas that would tend to capture materials, and last, make it out of SS or Bronze.

I have no idea how long it was in use previously. I've only had the boat for 2 years and have only put just over 50 engine hours on it. (I tend to sail in as much as possible and fire up the engine at the last minute.)

By using all new parts, I should get an idea of MTBF for the future.