It is common for some of the plastic gears in 1978 remote controlled R2D2s to crack. In order to fix these R2 units, I replaced the cracked gears with ones I 3D designed and printed. I would like to share these designs to assist with any potential repairing processes of other similar R2 units.
These designs were reversed engineered by measuring the dimensions of the broken gears with calibers. I have found that they work relatively well when printed properly and with the correct material.
Printing the designs very slowly on a raft with ABS seems to yield quality gears that are more robust than the originals. While I have printed these gears using a 0.4mm nozzle after some fussing with settings, a nozzle diameter < 0.4mm is recommended since these are relatively tiny prints.
STLs are provided for you to slice for your specific printer. However, if you need to make some tweaks to the designs (like for adjusting tolerances based on your printer's specs), you can use FreeCAD 0.20.2 or later, which is what I used to design the gears.