An autoparts chain has got Delvac 15W40 oil for $12.99 per gallon with Buy one get one free thru this week. My 04 250 SD 6.0 has used MC 15W40. What about this Mobil Delvac oil? How does it compare to other Dino oils like MC and Rotella? $6.50 per gallon is a pretty darn good price if the oil is any good??????????