470 antifreeze leak into bilge. Defective exhaust riser?

[matthysone]

while out on my first boat trip this season I heard an exhaust leak coming from back of the 470 engine. I assumed the rubber boot had come loose and upon investigating could see exhaust and water coming from this boot area. No big deal I thought just loose and the water was simply fresh water. However, upon trailering, green antifreeze poured from the bilge. The last trip out last year I had the same result but didn't hear an exhaust leak and could not locate any leak (no leak at the recirculator weep hole either). Last year I had a 3" heat exchanger and this year I have a 4", therefore problem is likely not with the exchanger. By the way, night and day difference with the 4" exchanger! The exhaust leak that developed today could be that I ran her WOT for an extended period to test the new heat exchanger. Had never been able to do that with the 3" for very long. Any ideas? Also is the exhaust riser the correct terminology for the part that the exhaust boot connects to?