Started replacing mine on Wednesday...finally got the broken bolt out of the exhaust manifold last night. My engine is a Yanmar 2QM so not only do I get to replace the elbow but also a flange that the elbow threads onto and then bolts to the manifold. Having enjoyed spending 12 hours trying to become a pretzel to access bolts, I also am replacing all hoses and clamps that are in the vicinity of the back of the motor and hope to not find myself down there again for a looooong time.
Note to self and others...when the wife mentions a new exhaust smell in the head and companionway...listen and investigate. My exhaust elbow had a crack that was more than six inches long. Fortunately it was in a place that was letting dangerous lethal gases enter into the interior and not gallons of seawater. And we thought the headaches were from too much rum the night before, possibly not. Once the elbow was removed, it is amazing to me that the engine was able to run at all, nearly completely clogged.