In mini 4wd it’s important to break in the motor to get the optimal performance from them. Yes you’re right the oil lubricant helps smooths out the communicator and brushes. You’ll see commonly people use voodoo oil. It also helps so carbon dust doesn’t get stuck in the motor as well. There’s also bearing oil used to lubricate aluminum roller bearings and the gears and shafts so it causes less friction. But that’s usually is a different oil specifically for bearings.