Checked the trim fluid in a friend's boat and it was full and milky. Water found it's way in there. There is no hydraulics at the drive. It can be lifted by hand with no resistance. Can the bottle be drained, lines flushed, bled, and possible work?
You can flush them, it's a mess but you have to take the lines loose and bleed the crap out or them. The tank probably got submerged. You'll have to do it bunch of times before you get all the water out of the system. You will also need to drain the tank a few times as well.