Yes. The key that is driven by the long slot in the lead screw is sheared off in the gear shown in your second and third photos. If you look down in the bore of the gear, you should be able to see where it used to be. People have dreamed up all manner of ways in which to fix it but personally, I would find a replacement. It won't be cheap.
Before calling Clausing, inspect the right lead screw bearing or carrier. If cracked or not an original, replace that as well. It was designed to break off if you have a crash and allow the lead screw to extract itself from the FWD-OFF-REV gear box. Or alternatively, you can modify the lathe by installing the 1 lb-ft slip clutch that was used on the final version of the 12".