Purchased a Norinco on one of the broker sites few days back, got it today and its an OK gun not as nice as advertised but still a good solid gun. One noticable problem though. After a really good cleaning the slide sticks right before the slide stop. I can ballance it there. I can shake the barrell lightly in all directions and then move the slide stop gentely and push the mag release and the slide will stay "stuck". If i shake the pistol the slide will release (all this is without a mag.). If I gentely push the rear or move the trigger it will release. Why does the slide "stick"??