From the look of things, only the nut needs replacing.
Stew-Mac has them, just like the one you have there, but I've got a better idea... I'll just give you one, free-of-charge. I bought it from Stew-Mac, but it didn't fit my truss rod. You should be able to remove the nut by simply unscrewing it (righty-tighty, lefty-loosey). A Phillips driver won't be very effective anymore, but a flathead between that remaining notch could work long enough to get it out.
