A friend of mine has run the Royal Purple 15-40 diesel oil in his 6.0 PSD. His OCI is 15,000. He has never done an analysis, but I have nugged him into letting me do one before he dumps the next batch out of his engine.
He tells me that he uses zero makeup oil between Oci's....wow, very good for a diesel or any engine if you ask me. I am trying to talk him into a bypass filter for extending his OCI's, but if the oil shows good @ 15K why bother. The only advantage is if the Ea type bypass removes soot and that would be an advantage for diesel engines.