I have 1984 mini, and the biting point of the clutch has gone right down to the floor and causing the gears to crunch!

I have bled the system, but with no effect.
So, i followed mr Haynes and tried adjusting the "throw out stop" (I think thats what its called) but again no effect.
One thing to note though, is that when adjusting the throwout, as soon as I move the plunger arm, even the tiniest amount by hand, then the clutch peddle immediately goes completely floppy with no resistance what so ever! Bleeding the system fixes it again.
Does this indicate a problem with the slave cylinder?