When I first started using Amsoil 49 years ago there was this one bottle for every application. I would suspect the biggest difference (if any) between the different applications today would be the label on the bottle. 3 0z. per. gallon is more than adequate and is what I run in my motors going back to the 1920’s. Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.