to others? Lately, I've noticed that Mobil Clean 5000 is consistantly priced much lower than Castrol and Valvoline... Only the Havoline is the lowest, but only beats out M-5000 by a few cents. M-5000 is 2.07/qt at Walmart while Castrol GTX is 2.46/qt. What gives? Speaking of brand name only, not the SuperTech.