Now that you say that, I dont think I have ever seen anyone have coolant in their exhaust due to a turbo seal. I have been around the SR game since the late 90's and nothing rings a bell. However if he just did a turbo swap and it was fine before, and it leaks now then maybe there is a leak from the turbo. I would assume the coolant ports are cast into the CHRA, maybe there is a possible crack, but you would think there would be oil contamination. Here is a good rebuild thread with an exploded view.
http://www.driftworks.com/forum/technical/60665-how-rebuild-your-t28-turbo.html