[rfeenstra]

Okay, so my curiosity got the best of me and I disassembled a 38-116 drive unit (no small task getting the unit out!)  Your analysis is correct, mine was wrong! The pictures that follow are of my unit disassembled. The fine tuning control was definitely made in 2 parts with the ball secured to the end somehow.  I cannot determine how they attached it so permanently.  I would think that solder would flow into the groove where they are joined and be obvious.  Perhaps they spin welded?????  Since that connection has to sustain torque of turning the shaft and the pull of someone removing the knob, it has to be a fairly secure joint.