Need pics of what he found, really, there's a HUGE difference between residual condensation and an actual "milkshake". Been a victim of both.
The above reference is pretty good, but it may also depend on how you run the boat. Understand water in the oil system of ANY engine is worse than dirt in most cases. I remember years ago, my ex-g/f had a new Quad4 Pontiac Grand Am, Quick little focker, but the oil was "milkshaked" quite often. We had the oil changed like every month because of my thoughts on it. Finally, I went to the dealer with her, and they said "Just the nature of it, it'll be fine". I got them to change the engine. Still did it. Traded it in on a Turbo Grand Prix.........

I'm sorry, theres a little bit of water that is BOUND to get in these engines due to what we do, but cannot be more water than a street engine in a rainstorm or driven through snow.......... So, to my mind, any water evidence in an engine needs to be looked into. Blown head gasket? Reversion through the headers? (Which can likely only happen with high lift and duration cams with a lot of overlap), on a BBF, bad timing cover gaskets?........I can go on and on. I've always been one to figure out the "why's" of everything. Sometimes the "why's" are ok and normal, sometimes not........
Leakdown test should test the head gaskets, other than that, never had the opportunity to try this, but thought of it before, drain the oil, hook up an air compressor to the oil pressure sending unit location and then the dipstick tube and start spraying the engine down with a dishsoap solution...........
Ray