Hi, i have a 2005 subaru forester x. the dealer which is kind of a long drive only uses castrol gtx, the last 2 oil changes have been 5w-30. i would change it myself but for warranty documentation purposes i'm gonna have it done.i would also use a synthetic but warranty states a 5w-30 @ 3,750 intervals,from what i've learned from this forum synthetic use would seem a waste of money for 3,750 .i've decided between the mobil clean 5,000, havoline, or mabey continuing using gtx .any suggestions would be welcome., thanks george