Get a new one. This is such a common problem on Mustangs it is likely that a junkyard bracket will have the same problem. A new one is not that expensive.
Yah, Just had the same problem on my GT. Went to autozone and bought new. Cost like $14.50 tax and all.
I would tend to agree that buying one from a junk/scrap yard will most likely put you at much higher odds for the same problem sooner rather than later, and it wouldn't be that much cheaper really.