I have a 2005 forester X and i'm considering changing the AT fluid using the drain/refill method 3 or 4 times as part of my 30,000 service. My manual says use Dexron III but I see that many newer subarus(5 speed AT) call for the special subaru ATF-HP which I assume is better. Even though my manual states DEXRON III, I would like to go with the best. Can I mix the ATF-HP with the dexron III that is currently in there now until it is evetually replaced with ATF-HP using the cycled drain/refill method. I understand its impossible to completely get rid of all the old fluid with this method but just wanted to understand if these both fluids are compatible.