seriously.. I just need to know if the Mobile 5w40 synthetic can be used in my 603.. it says its a stand in for regular 15w40... I want to stay synthetic but not with amsoil.. Amsoil just makes me thing "rednecks, stupid trucks, seriously overpriced, going out of my way to buy it".. I'm a Mobile user and I stick with what the sticker under the hood tells me to use. the autozoo has the synthetic mobile on the shelf and by the case so its easy to get