This is just not Castrol, it's also Valvoline, as Tom said it's two major PCMO that stand out in the past, and present as major oil companies occupying a lot of space shelf, and two of the most common name brand oils as well compared to a special mail order product (be it amsoil or anything) there is a difference...
Nothing bad meant towards amsoil, it's just not the same comparing this to amsoil.
Nothing bad meant towards amsoil, it's just not the same comparing this to amsoil.