Diskwarrior 4.1.1. saved the day. I used on a WD 500gb external hard drive and it worked like a charm - sort of. New users (like me) should note that the program needs to be saved into your applications folder, specifically UTILITIES folder (my first try kept giving me an error about changing permissions) but it was not necessary after getting it in the right folder.

Also newbies should know, when I did the first rebuild it came back with an error that it could not complete - I ran it again and it worked fine.

So while it has some learning curves, it did in the end do what it said it would do. I gave it a 4 out of 5 only because it required me to spend some extra time GOOGLING the problems I was having installing the program.

Now I can get back to work.... thank you DISKWARRIOR