Have you guys ever wondered why there isn't a fresh water flush built
into these systems?

This stuff doesn't corrode in the short time it's running. It
corrodes like this sitting there with salt in it...duhhh..

The problem isn't corrosion, per se. The heat exchanger is a bundle of bronze
tubes, and the expansion tank is aluminum (the better to radiate heat). Stuff
just gets plugged up and weak after a couple of decades. Recommended service
life is 10-15 years on the heat exchanger, and mine had served well over 20.
Just think, if I had a gas engine, even running exculsively in fresh water, I
would have been replacing the entire engine......for the second time. :-)