I pay attention to the spec more than conventional versus synthetic versus blend. The G37 calls for Dexron-VI, so that's what I use, and as far as I know, it's usually a blend. The old Audi called for expensive Pentosin synthetic, so that's what it got. I do fluid replacement in the G37. I never bothered in the Audi, given the size of the reservoir and the cost. When the rack leaked, it got a good flush before I resealed it anyhow.