This was wobbly and the client was unsure of what was causing it. I established that the main pivot was worn and arranged for a new socket to be welded on to provide the main shaft with a tight fit. This resolved the problem. Some while after a further problem was raised as the chair seat collapsed. Again on further inspection the shock mounts underneath the chair seat had become worn and were revolving too freely around the metal seat supports. New shock mounts were sourced from a specialist company in Denmark and fitted.