I have repaired several. You may not have the resource I do though. I have a whole box of the old telescopic antenna rods. I use a short section of the appropriate diameter rod, so with it flattened it will just slip over the slider shaft. I cut the shaft back, so the end is behind the slot in the face. I slide the flattened rod on the shaft, then flatten the part with no shaft in it a little more, so it is the same thickness as the pot shaft. I then fill the front flattened part with solder. I then put the face on, and mark the correct length of the shaft, then remove the rod segment and cut it to the correct length, and grind the sides down to fit in the knob. I then glue the rod segment back on the slide pot shaft with a little CA glue. It does take some time, but likely less than finding a replacement and then installing it.