The Yanmar exhaust mixing elbow is a weak spot for the motor.  It clogs and then performance decreases. At one point I couldn’t rev the motor over 1,500 RPM.  I cleaned it by soaking it in Apple cider vinegar which dissolves the carbon deposits but at some point the buildup is just too great.  So I purchased a stainless steel exhaust from a company called HDI Marine.  It’s a direct swap.  Here are pics of the new one as well as the old one.  Once I removed the old exhaust I looked at the water passage and saw that it was nearly 100% blocked!  Easy job…took about an hour taking my time.  While I was down there I adjusted my packing gland which seemed to be dripping quite a bit.  So a bit of maintenance done!