After experience with my Miata, I changed the tranny oil in my 8 today, after 9k miles. Used Redline MT-90 as per recommendation and the shifting is noticably better (not that it was bad before), just seems to glide through the gates with no notchiness. The drained oil was quite clean but there was a fair bit of iron mud on the magnetic plug. Also put Redline 75/90 GL 5/6 in the diff, can't say if it made a difference, but the car is running great and I can recommend the MT-90 highly for improved shifting.