Ok I have about 9500 miles on my '04 WRX. My first oil change was done with mobil 1 at about 3000k. I then hit 6000k and felt lazy so I went to a valvoline instant oil change place and paid for their synthetic oil change service... I walked out very happy with their service (although it was a little pricey). I am now at 9500k miles and wonder if I should keep driving and not worry about changing it for a while?? How long should I wait? Is it a big deal switching syn brands if I decide to go back to mobile 1 sometime in the future?