ATF for 08 Forrester

[Desaray]

Synthetic or regular old ATF fluid???...running this car in the heat mostly Florida and Texas and when I'm on the freeway I'm driving 90 miles an hour just wondering if synthetic is better in the heat or not?.. I usually throw in a bottle of lube guard also... I'll probably never do it again since it's at two hundred and ten thousand miles on it ....I think it's been changed maybe once before not sure ...if anybody knows if there's an advantage of synthetic or not???... might just get the Subaru fluid and chuck the the lubegard in there?....thanks!!!