Ran out of title space, but what I really want to know is this: How harmful is it to switch between brands of synthetic oil? I wouldn't care too much on my beaters, but this is my 2004 Forester XT (turbo). I would like to purchase oil that I get on sale proactively and in bulk, but I don't have the luxury of using more than one rebate at a time since I don't have any relatives. Any thoughts? Thanks!