My 05 STi is at 3000 miles now and need to change my oil. So I called the Subie dealer that i bought my STi from and asked them if i can use Mobil1 full syn. oil for the STi. They told me NOT to use ANY FULL SYN. oil for the Subie! They said use 5w-30 Castrol syn. blend only! If I use Mobile1 and something happen to the Sti it will not be cover under warrnty. Is this ture? Cause i didn't belive them, so I called another Subie dealer and asked the same question and this time its different. They said its ok to use any full Syn. oil for the Sti and I should use 5w-30 because here in Washington its pertty cold and also to put 4.5 quart of oil. So can you guys tell me who to belive. Thanks!