Take some of the oil and rub it between your fingers. It should smell like, well, oil. A crude oil smell, some oils like the old Castrol Edge (SM) have a sweeter smell like menthol (especially 0w20). If you have smelled a lot of oils and it is nastily different, you should probably not use it since there are so many GTX users on here that have not had this complaint.
You can always go to Castrol USA and have a "live chat" with some one.