A lot of fleets use 15w40. 15w40 is even touted as a oil for mixed gas/diesel fleets. The difference between 5w30 and 5w20 is about the same as whole milk and skim. Really. I have used 10w30, 5w30 and 5w20 without any noticeable difference. 5w20 is for Café standards and Ford specs 5w30 in about every other country for the same engines. My Dodge specs 5w20, yet they put a service bulletin, if you tow, to use 5w30. That doesn't give me much more faith in thin oil. Your always going to have the stringent rule followers and your always going to have the people that buck the system, in this case. Its not a big deal.