Awful grinding noise is back

[brisboats]

Could be the flywheel teeth are worn. Happens when water sits in the bilge and rust an area on the flywheel when boat sits unused. Starter pinion gear tries to engage the flywheel but grinds as the teeth are worn.
Hard to inspect the flywheel without removing the lower plate or starter.
Could also be that while your starter was loose the last time the pinion gear was worn from the excessive play. Each time you tried to start it that way resulted in wear to the starter pinion gear and the flywheel.
I would start by removing the starter and inspecting the pinion gear and shining a light where the starter mounts and inspecting the flywheel. Turn the motor at the crank pulley and inspect the flywheel all the way around. My guess is you will find your answer between those two.
B