Rotella in a 300E?

[alfa 75]

This morning I went to look at a 1992 300E for sale around here. Beautiful car, great color combo, transmission checks out okay, but the owner told me he uses Shell Rotella diesel oil in the engine.

I've always been under the impression that you should use diesel oil in diesel cars and gasoline oil in gasoline cars. Am I missing something here?

Edit: I may have posted in the wrong forum.. but I guess it pertains to a diesel oil.