I lube the gear reduction (planetary gear) section twice annually.
Wheel bearing grease, coating the teeth plus a small gob where gears mesh.
About every 1000 - 2000 miles, or if motor sound different.
I have separate eZips with 6000 miles, ~4000 miles, 2 with ~3500 miles all in good motor condition.
I've run 3500+ miles, overvolted as 36V -(42V full charge), motor still running great.
You can get the newer XYD-16 motor if you prefer a quieter ride.
Also capable or regearing for 20+ mph etc. See -
eZip - iZip re-gearing mods - 13T simplest