Probably got the leak from the shift cable bellows, usually the first to go. Have all the bellows replaced, as well as the water hose and the gimbal bearing. Don’t worry about the motor, do an oil and filter change, run the engine at mid RPMs for about half an hour, and then do another oil and filter change. As far as “tearing the engine down”, if it ain’t broke, don’t fix it.
If you have insurance that covers poor maintenance, call your agent. If not, **** it up.

I would do 2 oil changes and then run it for a few hours watching the temps. If you were in fresh water and it didn’t sit long enough to get a lot of silt in, it’s probably OK. Check your oil for foaming, and use a quality oil, but don’t go nuts with synthetics.

You may have to get into the starter if you think it got a lot of water in it.

If you have a good record with your insurance co, you might let them know so if the engine does go, they will cover it. Save a recites from the oil change and take pics of the bad seal and the repair bill for that.l

engine tear down… and no guarantee it will ever work correctly again