I believe the scratching comes from rapid descent or braking combined with gimbal/aircraft yaw or pitch during the descent. That will force the gimbal motor cover up into the L bracket and if you yaw or pitch the gimbal while rapidly descending it will cause the gimbal yaw motor cover to make contact with the L hook and scratch the cover.
Under normal flying conditions in non sport mode, and during gimbal autocalibration, the top of the gimbal yaw motor cover will never strike the L hook.
This is the plastic protective cover on a brand new gimbal.
This is the scratched yaw motor cover due to worn plastic protective cover after 50 flights, mostly in sport mode. After the L hook peels away the plastic it will start scratching your motor cover.