Maybe the slight difference in power required depending on rotational direction is due to the oil pumping method. In one direction the oil gets lifted up by one of the gears and thrown into the top of the oiling system. Thereby reducing the amount of oil resting in the sump. In the other direction it would not be lifting the oil into the oiling system but rather just thrashing the oil about. So the oil level remains high causing drag on the gear.
Or some other reason entirely. I also am not a mechanic.
