As users were still downloading this design even though it was broken I have decided to fix it.
It should now be identical to my updated design
https://www.printables.com/model/246505-updated-rc-car-differential-gearbox
which I'm using in my 4WD car
https://www.printables.com/model/281110-4wd-rc-car-185-parts
The author marked this model as their own original creation.