Can anyone out there answer why Valvoline MaxLife SemiSyn 5w-20 is Dexos approved while Castrol SemiSyn High Mileage 5w-20 is not? Do you think it's just a question of whether Castrol didn't want to go through the certification process and expense? Or, is there something about the Castrol that wouldn't allow it to get certified? Seems strange that both are semisynthetics, same weight and resource conserving and yet one is dexos approved and one isn't. Thanks for your help!