The leaf transmission is lacking a torque converter and therefore most of the heat normal autos have to deal with, no pump, no filter, no clutches, no bands, no hydraulic solenoids, no valve bodies, doesn not use multiple quarts of fluid, only has one speed, no "rubber band drive" as seen on CVT type transmissions.
About the only things a leaf transmission and an regular auto have in common is they both use oil, have drain plug magnets and have a parking lock.
Any oil that doesn't eat the seals and doesn't foam up like mad should work. Anything that would be put into an automatic transmission, differential or transfer case would be what you want.
"THE ABOVE POST CONTAINS MISLEADING AND INACCURATE INFORMATION. PLEASE CONSIDER IT OPINION, NOT FACT". -someone who I offended and is unable to produce the facts in question.