That's the bit that sits in the fork arm, between the arm and the ball thing it rests on.
Sounds like maybe the fork arm bent or, just wore through where the ball contacts it causing the slave to over extend. I had a similar problem on my 740 and as a temp measure I pushed the slave rod back in and pumped the clutch like 100 times to get some pressure back in and was able to move it about.
http://www.skandix.de/en/spare-parts...-fork/1019213/
If the arm isn't bent you might be able to buy that part and wiggle it in through the fork boot and onto the fork without taking the gearbox out, then bleed the slave and good to go!