Dodge Dart Pitman Arm

I have a 73 Dodge Dart, I was going to replace the pitman arm because there is a ton of play in the wheels when jacked up off the ground and slop in the pitman where it connects to the center link, but it looks fine to me the issue is that when I try to replace the castle nut and screw it back in the entire shaft turns? So I can't tighten it. Is this normal. I don't understand what could wear out on a pitman. Seems like I only need a new rubber washer, castle nut and cotter pin?

Thanks for any help on replacing or refurbing my pitman.