I just had my cars oil changed at my mazda dealership and i requested a full synthetic oil change and they did it then i got the invoice and didnt look at it til after i left and then realized it said they had put 5w20 synthetic oil in my car.. i called them back and they said they were 100% positive that they had put 5w30 synthetic in my car.. they asked the tech who serviced my car and he said he put 5w30 in.. i believe them but IF they had put 5w20 synthetic oil in my MS6 would it hurt?? or what would the effects of this be?? and how could i tell if they put one or the other in if its possible.