I pulled my copy of Robert Nitske's book, "Mercerdes-Benz Diesel Automobiles", to see if he had anything to say about how these cars were badged for different markets. He tells the story that in the USA the new 300D, as it was badged here, was a step up in terms of "luxury features", while in other markets the options between the 240D and other W115 cars were more or less the same so they called them 240D 3.0. I guess, then, that these cars came out during the time M-B began marketing their cars in the USA as upscale luxury items rather than simply as cars with different options like they did in the rest of the world.