After diagnosing with techs at LEAF they thought (for me) it is a problem with the Bellevue washers. These are cupped shaped washers that make up the spring that retains the driven gear in the gearbox, similar to the two stroke boxes.

I was sent these washers, the retainer half rings and all the lock washers and gaskets to do the install.

I'll take some photos of the job when I get to it, and post them here.