I changed to redline MT-90 for my transmission at 20k miles and while I haven't noticed too much of a difference, yet I have noticed that I have not been locked out of 3rd gear at all while at the track. I had problems with this before, I guess the new oil helps lube the synchros better allowing for smoother shifting. I got Mazda to do it while they changed my engine oil, and I think they charged me something like $20 for it. You will need 3 quarts for just the transmission.
