Here's some experience that might be useful to share.

We had an M25 Universal with an Oberdorfer raw water pump- which I liked better than the Sherwood because of ease of maintenance. But for several years, we had sporadic overheating issues with the engine. Despite change out of water pump impeller, gasket, cleaning the heat exchanger, pulling the riser apart, checking all the hoses, checking the antifreeze plumbing etc, the engine would periodically run hot. One day, to make maters even more frustrating, I noticed the overheat could be induced by turning the boat in one direction but not the other. A clew that made little sense. Finally, I noticed a tiny amount of wear in the bronze face plate of the pump- where it contacted the spinning impeller. The wear was almost imperceptible…maybe a .002-.003 inches had been worn away by the impeller rotating against the face plate. This tiny amount of material removed compromised the amount of suction in the pump. When the boat was turned in the wrong direction, the water pressure in that area of the hull was reduced to the point where the pump lost suction capacity. The pump had maybe 500 hours on it when the problem 1st occurred. For a few bucks, I had a machine shop grind the surface flat, and the pump has been perfectly normal ever since.
Hope this tip helps solve any similar mysteries.
Happy Sailing. Warmer weather is coming