Jon, as we talked about in the chatroom last night, saltwater is a particularly unfriendly liquid to have in the cylinders. I did the top on a Searay last summer that had been exposed to saltwater due to exhaust manifold problems. Even though the exhaust manifolds were replaced and the engine was thoroughly flushed the heads continued to corrode to the point where a valve grind was necessary. As I mentioned last night, I'd get the exhaust manifolds pressure-tested to be absolutely sure there isn't a problem there. Beyond that, I'd pull the heads to determine if there was a gasket-related issue, as well as to retouch the valve seats as a precaution against any corrosion issues. I'm sure you'll find the problem if you carefully inspect all gaskets and components when it's disassembled. If I can help in any way feel free to call me. Home # is 616-738-0474. Tell Nickslick he's welcome to call too.
P.S. Please keep in mind you can have a water issue on one bank of the engine, and have water migrate to the other cylinders through the intake while turning the engine over.

Jon, When I worked for a dealer w/a service dept. they had an engine take salt from the exhaust. Merc said to put in new oil and filter, run it for a few minutes, drain and repeat five or six times. This doesnt solve he problem of wher the water is coming from but that is what I heard you should do afterwords. Good luck. Whos boat? are you going to be in CA for the run next week?