Achilles heel

The little Mariner two stroke is a gallant little engine but it is prone to getting blockages in the cooling passages.
It’s not just salt, it is a kind of corrosion.
I have treated it with descaler (acid) and tomorrow will flush it out and put zinc chromate primer on the bits I can see in a faint hope of slowing the growth of aluminium hydroxide.
All this despite routinely flushing it out with fresh water every time it is used.