I have a 2005 forester X with the factory green coolant that is due to be changed. I have purchased prestone extended life antifreeze that claims to be safe with all vehicles and aluminum engines. I plan to add the required subaru conditioner as well and use distilled water in a 50/50 mix. The prestone antifreeze is phosphate and borax free so I am assuming it is the same quality green stuff that subaru sells. Am I safe with this antifreeze or is there something unique with the subaru green stuff and a reason to buy that instead?