Manual Transmission Fluid GL-5?

[note]

Hello,

Yet another manual transmission question:

As you know, our six speed transmission is the Aisin J160/AZ6. According to the owner's manual the fluid is 75W-90 GL-4 or GL-5.

Hoping to solve the problem with my first and second gears, which were very stiff on winter mornings, I replaced the fluid with a top-shelf product - Yacco BVX 1000 with GL-4 and GL-5 specifications.

However, the hard cold shifting remained. I later found out in some discussions that GL-5 is not recommended for this transmission as it contains some extreme pressure additives that can potentially eat away at the brass synchros. I asked Yacco and the answer was that they use "soft" technology that is safe for synchronized transmissions.

Do you think I should change the fluid again?

There are good reviews for Amsoil MTTG 75W-90, which is GL-4 and the technical bulletin shows "1B" for the copper corrosion test ASTM D130. Is this the best option I can find in Europe?

Thank you!

[ColinBarber]

Redline MT90 is an option.

Might be worth speaking to Opie Oils to see what they recommend.

[note]

So, after some research I switched to Motorcraft XT-M5-QS. The spec is GL-4.

It has very good reviews on several forums specifically for our gearbox. I also changed the transmission mount.

The shifting is now a bit smoother, especially from 1st to 2nd. Not a huge difference, but I can feel an improvement.