I purchased my WRX a few months back (mid-June). I changed the oil when I got the car (had about 31k miles on it). I have put about 4500 miles on the car since then and am still on the same oil. The car doesn't see really hard conditions and I don't drive it hard too much. I was planning to change my oil at 5k because 7500 seems to long to me. Anybody have an opinion on this that may help me? Also, does synthetic really make a difference?