Murray,
Why mess with something that works? Keep doing what you are doing.
I have been using good dino oil in my 2004 sprinter since the first oil change. People told me that my engine would disintegrate if I don't use the expensive synthetic oil. Well, I just turned 602,000 miles. No fuel and oil additives either. Oh, and oil changes every 15,000 miles. I had oil analyses done on the oil and I could still run the oil longer, but I decided to change it at 15k anyway. And on top of that, they told me that my engine is wearing less than the average of all their sprinters that they did oil analyses on.