I bought my 2015 wrx with 30,000 miles on it from the dealer. I just changed the oil and filter at 34,000 miles with 5w-30 subaru synthetic oil. In the future i am thinking of changing the oil every 3k miles just to be safe. I went with subaru synthetic oil but run valvoline full synthetic in my 2009 impreza 2.5i and it runs great at 102k miles. What are you guys using and how often do you change your oil? I love the oil filter in the engine bay too.