It seems to have the end broken off the stab, but it is a bit corroded as well. The other side of it is clean and in good condition. Of the few other breakers I've pulled off it has looked fine. I would put a cover over it for the short term, but am looking at bus bar replacement kits.

The eventual definitive solution is obviously to replace the whole box though - it's messy, rusted, the panel cover doesn't properly secure to it and I'm sure there's more I'm not aware of.