I'm surprise no one has mentioned the diesel's SCR exhaust fluid injection system. This is rather new, and was introduced first for the U.S. market, e.g., no long term real life experience at all, unlike the basic diesel engine design where BMW has been selling many diesels in Europe for many years.

I expect that the newly-designed SCR system introduced for the first time with the U.S. diesel has the most risk for long-term problems vs. the V8.