Problem 3: carbon buildup in the mixing elbow. Didn't know this until recently, but mixing elbows are supposed to be replaced as part of routine maintenance, after about 8 years +/- of service life. Ours was right around that 8 year mark, and had undergone some corrosion, and a fair amount of carbon buildup where the raw water interfaces with the exhaust. Replacing the mixing elbow with a new part fixed the problem.
There was a very knowledgeable lady at the Yanmar dealership in Oakland years ago where we went to purchase spares for the boat before leaving the country. She insisted that we purchase a mixing elbow. It wasn't even on my list.
Listening to her proved to be one of the smart things I did in preparing for that trip.
It was a hot, dirty job and my whole engine compartment was cover in soot, but at least I was able to fix it.
If I had a flow problem when heeling to one direction but not the other, the first thing I'd look at is how far you were healing, and what side of the boat your raw water intake is on.
That's exactly what I checked out first. There was no way the intake was out of the water. Though it may have gulped some air. It was pretty bouncy.
The thing is, after bypassing the strainer, the problem went away.
I have a new engine and the same strainer now but the hoses are led differently. I haven't experienced a recurrence of the problem yet, but I really haven't been it that rough of a situation with the new engine yet.