[6ragtop8]

I allways used 90w gear oil in my 70' Muncie 4sp, but I was with my brother-in-law when he bought a super T-10 for his camaro and the guy he bought it from told him to use ATF for smoother and faster shifts. That is what was in the tranny when he bought it. We were going to try it, but he sold the car before we got a chance.

[andyleonard]

We have used Redline MTL 90 manual transmission oil in the racecar's ST10 for 15 years.

In real life, you can run about anything that will keep the bearings wet, temperature willing, with varying degrees of synchromesh response. Some additives are too slippery and the gears will grind. Some are too grippy and the gears will grind. Some are just right.