Quote Originally Posted by Leonardomayo
I've found that, I've bought 2 and one had plastic gears and one had metal gears
Just swap one set of plastic gears with a set of metal gears and you'll have two motors each with a combination of metal and plastic gears, thus balancing them out rather than having one stronger and one weaker drive motor. Standard drills tend to come like this anyway; the metal stage is the one closest to the output shaft, and the plastic stage engages with the motor pinion.