If you buy an older I/O, water can back into the engine through the exhaust if you hang a kicker motor on the bracket, a cooler of fish on the transom, downriggers and a couple lard bodies on the lines. When the kicker is running the water will come into your main engine exhaust manifold and with no exhaust to blow it out it will flow in your cylinders through an open exhaust valve. When you go to start the main engine, it will turn a couple degrees and seize up since you can't compress a liquid in the cylinder. Your starter may blow, flywheel teeth will break, bend a rod or worse. The newer boats have overcome this secret fault by having wider transoms, but the older guys have this design defect. Be careful if you hang a kicker motor on a swingdown bracket on an older I/O.