I bought Motorcraft synthetic blend 5w-20 for my BULLITT now over a year ago, and never changed it. I know I probably should have, but only put just about 1,000 miles on it. Whats the deal with oil just sitting in the pan or in a sealed bottle going bad/shelf life? My question, is the oil in the bottle still good? Maybe I should go to a full synthetic because of my useage, what do you think?