[rfeenstra]

The outer housing has a hole in the side where a pin fits loosely (removable with a strong magnet, or in this case striking the unit on the side so that inertia would pull the pin out.)  This pin rides in the groove you see on the brass part with the gear on the end.  The fine tuning shaft is held in by the 3 ball bearings that ride on the ball bearing on the end of the fine tuning shaft.  That's why that little ball has to be strongly secured to the end of the shaft (how they did that is where our mystery is!).  To assemble this thing, you need to push the fine shaft in to compress the spring so that the 3 balls can be inserted all the way to the narrowest part of the groove.  This allows the brass shaft to be inserted into the outer housing.  Once the 3 balls are inside the outer housing, you can release the pressure on the fine tuning shaft and the 3 balls will expand outward and ride on the small ball on the end of the fine tuning shaft. Then you need to get the groove lined up with the hole and insert the pin.  The pin will hold the brass shaft in place.  The pin could fall out since it fits loosely.  It is held in place by another assembly that turns on this outer housing.  A fairly complex assembly as you can see by looking at the diagram that Morzh posted!

Since I had this unit apart, I cleaned it all up, re-lubed it, and assembled it with masking tape around the outer housing to hold the pin in. I should reinstall it in the radio chassis before I forget how the whole thing goes together!!