Joshua: Word of warning, I would bet you $100 that guy on the phone knows less about oil than you do, and it sounds like you don't know much! He is a salesman and will tell you anything! Talking about "special additives" is a load of BS. Ask him what the additive is so that you can make an informed decision.

GL-5 is a specification and does not dictate that Sulphur is used, but MOST GL-5 oils use sulphur in order to meet the spec.

If you are unsure, or uncomfortable try to return it.