Salt and polluted water corrosion has always been a problem, Even with non electric start motors. In 1956 one of my Michigan co-worker’s dad took a two week Florida vacation with a two year old Super Fastwin on a wood boat. He docked the boat at a salt water Marina. It had sat with the motor down for three days when he decided to go fishing. He noticed a oil slick on the water and when he tilted the motor up, the black spaghetti seal was hanging out of the side of the gear case. He said he felt a tingling sensation when he touched the motor. It turned out the neighboring boat had a battery charger plugged into a socket that was improperly wired. Such faulty wiring has been known to electrocute swimmers. It also proves that non-electric motors can be effected by corrosion.
If you are going to keep the boat in polluted water, mount a sacrificial zink anode on the outside of the transom below the water line. . . 😉
