Step 1: Ingredients
This time we are going to use these ingredients:
1) Plarepair (TM) powder (black)
This is 100% acrylic powder.
2) Plarepair(TM) liquid
This is Methyl methacrylate
3) "moulage you" (型取り君). mold plastics
It is low temperature deforming material, a kind of polyethylene resin.
3) Another old radio's knob for a prototype
4) A new general-purpose knob
It should be about 5mm smaller than prototype knob, and the hole diameter must be match the shaft of VR or rotary switch.
You can buy Plarepair here. And perhaps there are other products similar to it in your country.