Plenty of good advice. I had a similar experience several years ago, except I didn't have the excuse of a snapped
shackle. I was sailing with a friend and lifting the outboard from the tender onto the deck of the boat (a maneuvre I had performed numerous times) when it all went pear shaped. One of the tender
lines came loose and the tender moved away from the boat. To prevent both myself and the outboard (a 15hp Mariner) from going overboard, I had to drop the outboard. I watched aghast as it disappeared below the waves. Then imagine my surprise when it reappered briefly, buoyed up by the air trapped in the motor casing! Fortunately, I had the presence of mind to grab it and avoided the embarrassment of telling my friend that his engine was lost in 40 feet of water......
The old WD40 and drying out trick worked just fine and the outboard lived to tell the tale for many more years!
Stuart