If I'm understanding this right, the gear reducer in the Leaf is analogous to a transfer case in a 4x4 truck. In my Titan I changed the transfer case fluid (plain old ATF) about every other third engine oil change. The truck was running synthetic engine oil with lab testing at each oil change. The oil change interval was 10,000 miles.
The transfer case was a sealed system but unlike the transmission had no cooling system. The oil after 30,000 miles was downright nasty.
Teflon tape can be used on the threads of the drain/fill plugs. We used that on our transfer case plugs on the trucks with no issues, but eventually I just slapped the plugs back in without any further enhancements. No leakage over 100K miles there.
I'll be doing this fluid change soon. I didn't realize it was something we could maintain so many thanks to the OP of the thread for this information. I have a couple cases of AMSOil synthetic ATF leftover from my Titan that I've been wanting to use up and a couple bottles will work fine for the Leaf.
I have pump spouts on the ATF bottle. So I don't need to use a hose from above. At least I'm hoping it will work out that way.
2019 Leaf SV+ with Tech and Weather packages
2015 Leaf S (Totaled 10/2019)
2017 Ford F-350 CCLB 6.7L SRW 4x4