I was over at Napa the other day, and next to the M1 there were cheap-looking bottles of NAPA-distributed full synthetic in 5w-30 (green label), 10w-30 (blue label), and 15w-50 (getting familiar, red label).....what gives? Should I be spending $5/qt on M1 when NAPA is $3.49/qt? Is it the same formulation of Mobil 1, I should say?