I have known quite a few people who either have owned boats or still own them. I have never known anyone that was as obsessive about maintenance as my grandfather was with his boat. He always would follow all of the directions that came with the boat motor. He would use exactly the fuel that was recommended, exactly the right type of oil, and change parts when needed.
One time he got himself stranded on an island, because he had to have Optimax oil. He wouldn’t leave the island without it, but they didn’t have any. After that, he started carrying the oil that he needed with him, because he didn’t want to have to have someone rescue him again. Admittedly, the engine of his boat was always running very well, so being so being picky actually did help.