Re: curious about oil
jimlad,
You might frequent oil refiners/sellers/marketers web sites for your answer. They (some) will explain the differences in the requirements placed on the lubricants for applications such as OB, Snowmobile, motorcycle, lawnmower, weedeater, and all. I did and it gave me an education and I now use the proper oil.
I guess what you'll have to figure out is was it designed as an air cooled OB, or was it a spinoff from a motorcycle or something else to come up with the right answer.....or just email Brunswick.
My 2c,
Mark