Dunno, haven't checked. Starter turning over slowly as well, battery got submerged, starter got wet. Not sure where the problem is. Guess it would be a good time to take apart the starter and clean it...
Couldn't tell from the description whether this was the shift cable bellows as well as the drive shaft bellows. You can also get water into the boat through the shift cable
Yes, shifting is difficult with engine running or not. So does the starter need to be removed to access the shaft (guessing yes), and am I on the right track?
Seems like you have an expensive project boat there :)
I would simplify the wiring until you get it straight. Disconnect solar, physically isolate your house batteries, remove as many switches as possible, etc