I have a 2002 Windstar and I took it to have the oil changed. When I got home, my huband looked at the invoice and noticed that they had put 5-30w oil and he says it was supposed to take 5-20w. Is this a huge problem that needs to be corrected immediately, or can it slide this one time? My husband is all ready to start a big fight with the place and I just want to understand why. Thanks for any help.