Well outdated hmmm yes maybe. And then the japs know a thing or two about metallurgy and how to construct an engine. I work in the marine retail world and also supply Yanmar marine engines and spares. Yanmar do NOT aprove the use of CJ rated oils in their marine engines. Maybe they are concerned about the lower traditional antiwear additive content in the CJ oils. Maybe they are just out of date. Or maybe they are in to something. I tend to lean against the later when talking Yanmar. Take their recomendations dead serious! They know their stuff on diesel engines for sure. Then it is up to us to interpret the recomendations they give. But trust me, they do not give a warning based on being old fashioned and consrvative.
For what it is worth I have not looked into the specifications of the T6 Rotella 0W-40. So flame me for that if you want to. But for your own sake stick to Yanmars recomendations. It might pay off. And please do not start the "syntetic is allways superior" rage here, as it will not convince me. Why not an 15W-40 HDEO CI spec oil unless you are running in arctic conditions???
Motorsen