chris42pu,
This is "closing the gate after the horse is gone" but, I've found that approaching old bleeder screws with a GOOD SIX-POINT, 1/4 drive socket (SAE or Metric, whichever fits best!)and GENTLY rocking, first "tightening", then "loosening" ever so slightly, until you feel the screw free-up.
(A good soaking with PB Blaster beforehand helps.)
Usually, the first "tightening" action breaks the screw free, and it loosens-up pretty good.
I 've had good result with this method, but a good part of its sucess is contingent upon your own ability to sense when a bolt about to snap-off; having broken many in my lifetime, I've learned to be careful.
If someone's already round the hex off the screw, you can try the same approach with a GOOD pair of Vise-Grips (works easier with the cyl in a good vise); the screw is usually "toast" by this point, but replacement screws aren't hard to get.
Good luck!
