You know I have to jump in on this one.. SYNTHETIC oil works WONDERS compared to regular "conventional oil"... Trans fluids differ in characteristics,,, different scrubbers and different surfactants to work in an automatic transmissions enviornment, since your gearbox isn't an automatic transmission, and doesn't have friction and steel clutch discs, ANY ATF will do the job!!! There are anti foaming additives in ATF that differ between types,,but,,,your chain isn't going THAT FAST that it would make a difference.. ATF is equivalent to a 10 weight motor oil...gearlube is usually equivalent to a 90 wt motor oil... when its 10 below outside, 90 weight is equivalent to WHEEL BEARING GREASE and ATF equivalent to 30wt motor oil... so you see,, ATF is a FAR BETTER CHOICE than gear lube,,, ATF will leak out faster if you have a sled with a LOT OF MILES and your seals leak,,but,,,usually ATF has better lubrication qualities with radial lip seals than 90 weight does!!! Now if you DO NOTICE small leaks when changing from 90 weight to ATF, you can always add a SMALL AMOUNT of DOT3 or DOT4 (not silicone) brake fluid, and that will swell up the seals and stop the leaks!!!! ( a SMALL AMOUNT is about 1/2 ounce).. Do NOT ADD brake fluid if there is NO LEAKS to begin with.. while swelling up seals is a good thing (to a bad seal), swelling up a seal that doesn't need to be swelled up will prematurely wear out the seal because of the expansion of the seal due to the brake fluid!!! DON'T swell them if you don't need to (is my point)... Personally, I use synergyn on all my stuff (sleds and race car). I am not interested in making the land speed record on a sled (anymore) and the trails i ride onhave a speed limit. ( I am also getting tired of giving the government my money for snowmobile tickets).. Gary Oles nosboy