(PLEASE NOTE: old oil shown in photo is the old genuine Mazda fluid! It is NOT used Redline oil.) I used it in my 2010 Mazdaspeed3 with around 75,000 original miles. I changed it myself, shops in the area didn't want to bother with it. The original trans oil had never been changed (quite simply because, Mazda claims the original factory fluid is a "lifetime" fluid, which it is obviously NOT), and came out of the car looking dark as cocacola, and thick as (real) maple syrup. Whereas this new liquid is transparent, with the slightest hint of red, and flows quite a bit easier than the old, nasty black fluid. Before I changed it, I was having serious issues getting stuck shifting into 1st and 2nd (the shifter often wouldn't want to move all the way into gear). It was so bad that I was considering getting rid of the car. But this new oil fixed it 100%. With the old oil I also had an issue with 2nd gear going in with a crunch (worn synchro probably?), this oil didn't completely eliminate that crunch but it reduced it a lot, and now it goes away completely when the car is fully warmed up. I still can't believe Mazda doesn't have a service interval for changing the transmission fluid in the speed3. This fluid absolutely needs to be changed.

As for how to change it in the Mazdaspeed3: https://www.youtube.com/watch?v=yWMk_Q1pE8c
Tip: If you can manage to find a funnel long enough, or extend the one you have, then you won't need to remove the airbox. I extended mine with a plastic water hose.

It is what my son needed and at a good price

I used this in my 2011 mazdaspeed 3 and it works great. I don't have any issues with the transmission that it could fix for me, but it is just as smooth shifting as before.

I bought a high mileage 2017 MX-5 RF Club and recently hit the 52k mile service interval which included the transmission and differential fluid. I generally like Mobil 1 full synthetics and used that in the diff but they didn't have a GL-4 rated fluid and was warned in the forums that GL-5 can be bad for transmissions with copper alloys (brass). So I got the Redline MTL that everyone recommended. Amazing stuff. Not sure how much was fresh oil and how much was the MTL but defiantly shifts more smoothly, particularly in the cold.

Decent price on the gear oil for my nv4500