Gearbox will need to be dropped, may as well change clutch while you are there.
Replace parts 1,2 and 3 in this diagram. Its what the clutch release bearing slides on, it becomes scored and rough and the bearing no longer slides smoothly leading to the clutch dragging or slurring...
This part should be replaced each time the clutch is replaced!
Make sure to replace the bearing as well, should come with the new clutch kit.
Then follow NZ's description. On resetting clutch values/ curve etc.
http://www.realoem.com/bmw/showparts...19&hg=23&fg=15
Simples