ATF can be corrosive to metals and certain rubber seals. The transmissions that use it are designed for its properties. Chain cases are more similar to differentials with 75w-90.
But I agree with BC_DAN. It really doesn't matter. If you run vegatable cooking oil, you will get the exact same life as someone with $$$ factory oil. (as long as the ATF doesn't eat your seals and leak out at least, that would be the * in the story.)
1) 2000 Arctic cat ZR 700, which now thinks it is a 2001 ZR 600 EFI APV w/136" ripsaw. (for sale!)
2) 1995 Yamaha VMAX 600, which now thinks it is a Polaris! (Polaris x10 suspension, Polaris P85 clutch) (for sale!)
3) 2004 Yamaha Warrior
4) 2006 Yamaha Nytro