The radio is a Sapphire XXIII and from what I can tell, the guts are similiar for most of the Sapphire models. The green toothed gear that is connected to the tuning knob broke. I have no idea whether this part can be replaced or even repaired, the plastic is pretty brittle. Everything else works fine, just can't use the tuning knob.

Anyone have experience with this ?

I had the same problem with my radio and I sent mine to D and M restoration and they cleaned and repaired it. Came back looking like new.

http://dandmrestoration.com/services/radio-repair/