securing thr main tuning knob ?

Having just bought an FT 100D, the main tuning knob is loose and wobbley but still works to change freqs with no problem. I want to know how the knob is attached to the brass threaded channel that goes into the encoder? mine is attached with a round spring but does not " pullin" enough to fully seat the knob. that's all I can find on this radio that is used to hold it together. Seems like its missing a part or so. Anybody have an exploded view of the encoder with attachment parts and parts that secure it?
                                        Thanks John   KF7OM