I've heard of alot of people using ATF with good results, but have to change it all the time. I have been using Amsoil's Formula 4-stroke 0w-40 for several years now and it seems to work great. I started racing at the beginning of the year, and honestly, I don't have to change it that often. The oil doesn't get dirtied up or have particles in it very quickly. I have great clutch engagement and go several races and fluid still looks good. I have changed it a couple of times in the past thinking surely it should be ready to be changed by now, and empty the fluid and it still looks a light golden honey color with very little amount of particles in it. It is more expensive than ATF, but it keeps me from having to change it very often and it protects the gears very well. Just my 2 cents.