While the exhaust elbow from the outside looks pretty large, there is a water spray baffle inside which seems to build up a coal like coating eventually blocking the exhaust completely.
first symptom in my last case was increasing soot in exhaust water, then black smoke, then the engine actally will run at lower revs only, then it will start and die. I'm thinking this is an every 5 year job on #505 now that it is down in FL. 15 years when it was in NPT. relates to engine time running. 300 hours maybe?
In earlier case where I thought it was an impellor problem, it actually had carbon blocking the water into the elbow.
... when did you replace the elbow last?
I'm sorry I didn't think to get shots of the sooty water and smoke on video, but I did get the "fixed" results in this video ...
