I was always too lazy to research the correct coolant. So I'd go to the Subaru dealer and buy OEM with a bottle of conditioner (it's basically stop leak). I think it cost like 32 cents more than prestone at auto zone. That's ok.....I had suby bucks and picked up other stuff while I was there.
Remember to use distalled water. Not spring water, not boiled water, not tap water, not soda water, not scotch and water. CVS has it cheap enough. Distilled water doesn't have minerals and crap to mess up your cooling system like all that other water does.