I used sta lube GL-4. I finished the conversion about a week ago so the fluid that I drained out was fresh. I replaced it with Valvoline Dexron 3. I did a little research on the effects of atf on the synchros and didn't come up with much regarding damage/corrosion. I'm sure that a properly maintained trans with GL-4 will last a long time. I prefer to follow the factory recommended lubricants, but just couldn't handle the stiff shifting for the first few miles and the atf completely eliminated that.