ATF gets nasty looking when it's not in a transmission. There's no filter in the Leaf gearbox, just like a transfer case on a 4x4 has no filter. There's no cooling mechanism in a transfer case. So the fluid tends to get dark. Modern synthetic ATF is hardy stuff that can handle some fairly high temperatures. Like well above 250° F.knightmb wrote: ↑Fri Sep 18, 2020 7:57 pmAlso note, didn't change mine until 66K miles, so it's possible it didn't really gain efficiencty, but just returned to what it was new since the stuff was very dark and dirty when I changed it, plus a lot of the metal fragments seen in the pictures posted here when others changed their gear fluid.
It would be interesting to have the used fluid tested to see how the viscosity compares to new fluid.