Unless you do a considerable number of short hops, a 4K oil change interval should work well. Using Rotella in one of these engines is not a bad plan either. Flat tappet cam engines need ZDDP additive for cam and lifter life. Todays passenger car oils don't have it due to the vast majority of cars having roller cam followers these days.

Thanks to the latest emissions pressure on diesel engine oil, the ZDDP content in the the diesel oils such as Rotella has decreased. Since, however, this is a sliding follower system, the amount of ZDDP in the latest Rotella should be adequate.

The vast majority of the miles on my 300E have been with Chevron Delo, the Chevron equivalent of Rotella. I personally would NOT run any of the newer passenger car oils in the M103, especially in the super lightweights that so many modern engines successfully use.