I was setting up my new NN5 on my old Bogen 3205 and noticed the center column moving slightly as I rotated the camera.
At first I thought something was loose.
Then I noticed the gap between the legs and the underside of the base caused by the O-ring.
I removed it and the base now sits firmly on the legs.
Not sure if other tripods have this, but if they do, see if it removing it doesn't make it more sturdy.