Remove the right splash shield in the wheel well.  Turn the front
wheels to the left and you will have enough room to access two
phillips head screws that partially hold it in.  One of the screws is
easy to see and the other is on the bottom of the fender (if you lay
on the ground, it is about two inches back along the frame).  Once you
have these two screws out,  you can pry the splashshield toward the
tire and access the antenn motor assembly.  Ther is only one bolt, I
believe 5/16, that holds the assembly to the frame.  Once it is
removed, you can set the antenna assembly on the tire and remove a
bolt (3/8?) to disassemble the mechanism.  It is pretty simple to find
the broken antenna mast. Reassemble the antenna motor/drive.  Then
have someone turn on and off your radio to help you feed the new mast
into the reassembled unit.