Re: 1981 15hp johnson seahorse
Your outboard is a two cycle engine. The oil is mixed in with the gas. The only "oil" your engine has is the gearbox oil, which is usually changed every season or so, or more frequently if it leaks water. I'd advise changing the lower unit oil if you haven't this season. There are two screws int he lower end of the lower unit. One near the bottom, big flat head screw, and one somewhere above or below the anticavitation plate.