I have noticed on my 4x4 front axle that there is a grease seal pressed in the steering knuckle behind the front wheel bearing that the axle fits into. There was a little grease in there when I removed the axle and bearing. Is this area supposed to be greased around the area between the steering knuckle and the axle, or is that seal just a dust cap? If greased, how much...fill the space between the wall of the axle and the wall of the steering knuckle?