Brett: After much research and hand-wringing, I decided to delay the switch to synthetic oil on my 2005 WRX STi until I hit the 10,000 mile mark. Up until that time I changed the oil and filter every 2,500 miles with either conventional oil (Mobil Drive Clean 5w-30) or semi-synthetic (Motorcraft Semi-Synthetic 5w-30 & Mobil 7500 Semi-Synthetic 10w-30). At the 10,000 mile mark I made the switch over to Castrol Syntec 0w-30 (aka, "German Castrol" or "GC"). I'm planning on running it for 5,000 miles and will have Blackstone Labs perform a UOA on the oil at that time (all my previous UOA's can be found here on BITOG in the UOA forum).
Congrats on the new ride!
