my 95 did the same thing a few months ago.
Ibled the brakes over and over but it would eventually start to fall to the floor again after afew miles. the master cylinder would have to fail very badly to get fluid on the pushrod,so bleeding wouldnt make them work even for allittle while.
If you chang the master cylinder your self when youre putting the new one in thread the lines first before you put the cylinder on the screw posts it makes the job easier as you wont have to pull on the lines so much.