In my work, I have removed the mixing elbor. Upon inspection, the water intake port was 50% blocked with gook. Also, the front of the elbow was paper thin on the exhaust side of the loop and broke through with a strong push of the finger.....That is why Yanmar suggests changing every 5-years I guess....not 20 as in my case. I have some pictures I will post later.GregP36-2 #101