im a castrol guy.....whats the differance who really knows, all you can do is read and try products, i have had a lot of turbo and oil cooled cars, thats what seems to work the best for me , and i have been using   "lucas" oil additive for the last 15 years too....

Good article.  Workhorse Custom Chassis uses the Chevrolet 8.1L in there motorhome chassis and has stated that they don't want owners/shops to use the 15w/40 diesel oil in there engines due to problems with rings   

I'm going to use the straight 30wt oil when I change my oil this next time.  If I had more time I would change it before this next trip because I don't know whats in it (oil was like new when I picked up the boat).