its blown, replace it.

BTW gravity bleeding works quite well on a lot of vehicles. I just replaced the master in my '91 Si along with the front rotors and pads. I replaced the master without getting any air in the lines too, its actually rather easy and eliminates the need to bleed the system when installing a new master cylinder. However I bled my system anyway just to purge out all the cruddy old fluid. Since I had a buddy to help we didn't bother gravity bleeding. However I did just replace most of the metal and rubber brake lines on an '85 GMC 6000 full-size school bus Friday and gravity bleeding worked like a charm on that bad boy. Talk about some serious brakes. The master cylinder resevoir holds a gallon of hydraulic fluid!