I'd have replaced the plastic ones with plastic,if they had been available. The plastic ones lasted 4500 miles. The same motor is not available from the source although ebikeling still sells power wheels with geared hub motors. He's decided 48 v geared hub motors are a mistake.
Not a lot of repair parts for hub motors. Luna had some gears for a bafang geared hub once, but they didn't specify which one and they never sold a thin tire bafang motor when I was shopping. Just fat tire motors.
You even have a vernier or dial caliper to measure the gear? About 5 dimensions to get right on a replacement gear. OD, root diameter, shaft diameter, thickness, # of teeth, helical or straight teeth, what spiral value.
I haven't seen very many dimensions listed on bike parts. Shimano Sram & sun don't even provide dimension charts for their freewheels and sprocket clusters. Not even sprocket thickness which is obviously different for different width chains.