I had an incident on the lake last weekend. Not quite sure of root cause at this point but the boat was overheating. I shut the boat down and got it home. I pulled all the plugs. 7 of 8 of them were perfect and dry. However, once I removed one of the plugs.....water poured out.

Can anyone help me with troubleshooting this? Logical steps to walk through?

Manifold leak !! or cracked head !! ???

I would check exhaust manifold first !

When you say manifold, you are talking exhaust manifold? Same as a "riser"?

The riser is the piece bolted to the top of the manifold.

it sound like you may have done a head gasket.

logical steps,

remove plugs,
do a compression test,
if that is inconclusive do a leak down test. that should identify gasket, piston or valve problems.

if those tests are good pressure test the exhaust and risers.

is this a closed cooling motor?

and it doesn't matter at all right this minute. what you have to do instantly is fill that cylinder w/ wd40 and get the valves oiled down or in the next VERY short period of time, the rings on that piston are going to rust to the piston , the bore will rust and the valve stems will rust to the guide... all of which will take a minor repair right now and turn it into a monster repair by the end of the week.

that is a fact

CRAP! I was afraid of that. Motor has been sitting for 14 days.

still better go do it. you might be the luckiest person in the galaxy... you never know.

I can personally verify that...I'm about 30 minutes away from having the chain hooked to my engine. I'll be replacing my rings...heads are in the machine shop right now. If all goes well, I'll have it back up & running by the weekend...& I do feel like I was very lucky.
BTW...Both CMI Headers tested perfect with air & water test.

Good Luck...