If you are really convinced about the C* rating, Valvoline VR1 Racing Oil has a SJ/CD/SH API rating. It comes in different grades, 40, 50 and 20W-50 which I use in my '80 300D oil burner. I'm kinda sold on the C* thing also and after trying many other oils, I am most comfortable with this one. Maybe its just the power of suggestion but my engine seems to run smoother. You can get it at Walmart for about $1.69 @ qt.
Would it be a bad idea to use 40 or 50 in summer to decrease oil consumption?