I changed the oil and filter. Saw no signs of water in the oil.
Pulled the glow plugs and bumped the starter. Got a geyser of water from one cylinder that hit the rafters of the barn 15 feet overhead. The other three cylinders gave up weak little sputters of water. After bumping the starter about 4 or 5 times, all I got was diesel. Hit it another 4 times to ensure a good coating of diesel in each cylinder. Shut it down. Overfilled the oil to coat as much as possible. Let it sit for a few days.
Today I drained the oil down to the correct levels and tried to start it. After about three minutes of cranking, the battery started to fade.
I pulled the pickup around and jumpered the batteries.
Another minute of cranking. Suddenly, vroom or however you describe that sound in a diesel engine.
Hallelujah! Purring like a kitten. It blew a spattering of water drops out the exhaust for a few minutes, then that stopped.
I hooked up the bushhog to check it with a load. Two hours of mowing later, not a single hitch in the giddyup.
I firmly believe the Good Lord protected me from my own foolishness. It seems I will avoid a major repair bill.