I recently picked up an '05 GT with 141K and what turned out to be a new(ish) motor. Overall, pretty happy with the car. Yes, it has the power of a Miata and gets the gas mileage of a blown hemi, but I like the handling, it looks great, and provides a unique driving experience.

One problem I had was grinding into 2nd and 3rd when the car was warm. Upshifting or downshifting would grind at anything north of 5K. When I replaced the gearbox oil with MT-90, the problem went away within about 25 km. Now, no grinds when upshifting even at redline, and as long as I'm patient and deliberate with double-clutch downshifting, I now have no grinds going down to second at high rpm either.

Having been previously underwhelmed by Redline products in other cars, I would not have thought a gear box oil could make this big a difference; seems a little too snake-oily methinks.

So, thank you, you gorgeous forum bastards, for finding out about this glorious wonder oil, and saving me the $500 for a new (used) gearbox.

Praise be to Jebus.

 

Glad you got it fixed but replacing it with stock fluid would have yielded the same results.

 

Good to know. I can't render an opinion on the stock fluid as the removed gear oil was of unknown lineage, but the Redline worked great.

 

It should be fine for a while but be prepared for synchro issues in the future. New fluid will help for a while though.

 

IIRC, you replaced your box with an S2 box, did you not? Any better after living with it for a while?

 

Yeah, my original trans lasted about 124,000 miles and was working fine but I would have to change the fluid more often towards the end since when the fluid would age, a slight grind on down shifts would come back.

My S2 trans only had 9000 miles on it when installed and I only drive it on the weekends now so no complaints. A few of us locally have S2 transmissions and no one has any any issues.

But I do feel the S1 transmission issues are largely due to those who can't drive a manual properly if the car is not tracked or neglected.

 

I have only used OEM Mazda gear oil in the RX-8 But Redline stuff is great.

 

I changed my OEM oil to Redline MT-90 at 20K miles. Compared to Redline, the OEM oil felt like shifting through molasses. At 38K miles, I inspected the trans oil, and it was still pink and perfect. I really like Redline. But, the OP obviously has synchro issues, and the improved oil will only mask them for so long. Who knows? Maybe so long will be long enough.