guys, i have new fit aria 2008 i'm going to do my first service in next week. i'm going to do it with stafford, i'm in trouble to find good engine oil for it. one of friend said castrol magnatec or gtx is good but im confused with this synthetic level, 5w-20, 10w-40 etc. i even ask from stafford they said any will go with it but im dought that, can you experts help me on this ?