This thread could use a bump...
Seems very rare to find info about this necessity here, really the only "wear" part on the Leaf.
I'm at 60K miles on my Leaf now - and between the towing, speeding, and everyday highway miles, they're some rough damn miles. I'm definitely interested in taking care of the reduction gear oil, but also interested in doing it myself.
It sounds like the plugs should be relatively easy to find, though angling to get the new fluid in there may be challenging. In the service manual, it says the plug gasket should be changed any time it's removed.
The gasket is part number 110264N200 (via Nissan parts lookup site). Googling shows a few parts available through Amazon, eBay and other sellers, but not very common (e.g. no Amazon Prime and no free shipping on most places), but still easily available for under $10.
The fluid is "Genuine NISSAN Matic Fluid S". Actually sold by Amazon and available with Prime -> https://amzn.com/B005ETHNFC
Worth it? Maybe I'll even do a video.