Water in manifolds

[speedysprocket]

So I replaced all four of my exhaust manifolds this summer with Mercruiser manifolds, not aftermarket, because of all the stuff I read about them not being flat and such.
Well now I’m rebuilding my heads because I didn’t like the compression numbers I was getting.
When I’ve pulled each manifold off, there’s been a little water in at least a couple of the exhaust runners on each manifold.
My machine shop said when he cut the seat in the first set of heads, he could tell there was some slight pitting or corrosion in the seats. So the water in the manifolds would explain the pitting.
Is there an expectation that being a boat, some amount of moisture is going to collect in the exhaust? I use good gaskets, and my elbows are stainless, so I’ve never questioned them, but I’ll inspect them closer while they’re off now.