[RodB]

As you can see, mine has a chunk of hard rubber remnant on the shaft next to the chassis. I would say the shaft was, at one time, covered with the rubber to provide appropriate friction for the string. My take on this is to clean the shaft, then put heat shrink on the shaft, shrink it and put the string back. Simple fix and it should last much longer than original.
   

Here's the antenna photo.
   

You can probably build one with 14 gauge copper wire.