Why can't I just use MT-90
 

The FSM calls for API GL-4 75w-90 gear oil for the 6MT...and Redline MT-90 is GL-4 75w-90. So why do people mix the MT-90 and MTL for the Z's trans??

i think many just go with mt-90, ive seen no reported problems. i just started doing some research on this matter.

I've also just started researching this beaten-to-death subject as I just had my tranny replaced. For some reason I think I'm leaning more toward the royal purple then redline. It seems from my research that not as many people complain about problems not being fixed w/ RP as there are w/ the Redline. (Notchiness, noises, etc.) Still not sure though.... :thinking:

i've been using royal purple since my tranny was replaced for the 2nd time (about 20k miles) and have not encountered a problem it actually made it shift a bit smoother.

everything ive read about rp tranny fluid has been positive, cant say the same about redline.

i actually use royal purple in the rear diff as well and its quieted it down quite a bit as well.

Actually, the FSM calls for API GL-4 75w-85 gear oil. That's why a mix of MTL and MT-90 will bring the viscocity to factory specs. It's also what Redline recommends for the Z.

you can use the MT-90 without a problem. Like dkmura said, you mix em to to bring the viscocity to factory specs.

85 / 90 difference... no biggie. especially if you live in warmer climate zones. don't even bother with mixing... just straight pouring with the MT90. oh and you need a swedish pump to get the job done, lol.

I also use the Royal Purple in the tranny and diff. Everything flows like butter