I just bought a new wrx tr. I met the service manager after the buy and after I told him I would do all my own oil changes, he told me to keep oil and oil filter receipts and not to waste money on a full synthetic oil. He said the 5w30 you should use year round is part synthetic to meet the SM rating anways. He also went to explain that except for kendall, the oil companies dont want people to know this. He also said not to use mobil1 gear lube in the tranny because they once offered it and got a few shifting complaints with it. So am I being cheap if I would use castrol 5w30 and a purolater oil filter every 3750 miles?