I worked on a 6 cylinder 2 stroke Supercharged Diesel Detroit 71 Series engine once in a grader in Methven New Zealand.

Farmer had left it sitting for a year or so in a field with nothing over the exhaust stack, centre 2 cylinders had filled with water. He tried to start it and nothing happened, so he got 2 brand new batteries, sill nothing. He then had the starter rebuilt and tried again. He sheared the flywheel bolts clean off of the crank.

We had to drill them out and do a full strip down of the engine, replace some liners and a few pistons and she started right back up.

So in short, water in engine is seriously bad. Take sump of as that's much easier than head on that engine.