So I have been running Delo 15w40 LE since I have had my 7.3 for over 6 years now. I see that Ford has not recommended the CK4 spec for any engine old or new and that Fords own testing has shown it to not have the antiwear properties of CJ4 spec oils. I now see that most oils on the shelf are now CK4 including the Delo I have had great success with. So for now I'll put some motorcraft oil in and hope that a few other oils keep the CJ4 spec.