My brother just purchased said vehicle with no owner's manual. It appears Subaru has a regular ATF and an ATF-HP. It seems around 2005 ATF fluids change. What is the best option for a partial drain and refill?
Valvoline MaxLife DEX/MERC lists as being suitable for "Subaru ATF and ATF-HP applications" and is a good ATF. With that said, I have no first-hand knowledge of whether Subaru transmissions do well with it or not.