Bushing on shaft under mechanical advance?

Is there supposed to be a bushing on the distributor shaft underneath the mechanical advance mechanism? I have about a 1/4 inch of play and the advance mechanism has wore a groove in the bottom inside the distributor housing. When I was moving the distributor around before I was going to drop in rebuilt motor piece of plastic fell out. So I disassembled and found groves and noticed up and down play. Sorry no pics:(