I don't keep any receipts but I will send in for oil analysis just for my own information. I'm not too worried about the dealer denying any claim and the burden is on them to prove you did something wrong, you will never have to prove you did something right in court under magnuson warranty rights. The dealer may require you to show receipts, that is a fact, but once you file a law suit watch how quick they buckle and they will be liable for more then just fixing your truck, and that is a fact as well. They cannot legally deny a legal warranty issue, they are the ones at risk when they do so. They get away with it because most consumers wont fight.