I've got about 17k on the car. Dealer did a half flush thing (idk) with about 4-5 quarts (i made sure he didn't use z1, but the best around was MOBIL 1). anyway, when should I do my next drain/fill? I know A/T don't enjoy the redline much and I do frequent that territory so I'd like to keep it good and fresh. Also, which type of fluid is good?