Never really had any problems with Castrol. I bought this '69 Firebird with the 305( would not be my first choice, but that's what it came with), and not sure whats it's been through. Saw where Lucas was supposed to help "older" motors. A guy at work who has worked on cars, built race cars"all his life", swears by Lucas. Told me that putting 1 qt lucas with the Castrol was "perfect". Like Don Henley said " the more I know, the less I understand.) Kelly