Might be worth your while just to ditch them, particualrly if they have turned a rich brown colour. If had such brass fail.
I figured the brass was attacked chemically, or had hardenned in the extreem over time, to the point it was brittle, as when fired the brass developed little holes in the shoulder area of the case.
Granted, I was trying to fire form this particular brass, but the affect was startling. It looked like a tiny guy on the inside of the case has fired a shotgun through the case shoulder.