Propshaft, not crankshaft.

Crankshaft is inside the engine, propshaft connects the transmission to the prop.
Id check the packing where the propshaft goes through the hull, I know mine was leaking pretty badly until I replaced it ~2-3 years ago. Now its much better, hardly get any water in the bilge (unless one of the drain cocks isnt fully sealed, check that too!).
Let us know what you find out.