I've heard that Castrol is the purest oil out there from a friend of mine. He said he's disassembled engines that have used Havoline, Penzoil, Valvoline, and Quaker State for years and found a lot of parrafin buildup. He swears by Castrol because he's never had that happen with any cars that use it. Any similar experiences? Wanna kill these ads? We can help!