[Thealien]

If the captive nuts are no longer serviceable could you remove or drill the bad ones out and just use a nut!

Those captive nuts are held in similar to door hinges so the nuts/plates have some movement or at least that’s how they are on my 1972 Blazer(s). When you look up under the rail you should be able to see them. You would need to remove the bedside trim panels to see them. Not sure how to explain but you could cut one end of the captive assembly so you could slide the old threaded piece out and slide a new one in. If you were carefull cutting the end there could be enough material to fold back over and keep it from falling out?