Getting the clutch master cylinder off is a bear.
I did this on an 82 320is - the easiest way is to order a rebuild kit (NAPA), and replace all the master cylinder internals from inside the car after removing the clutch pedal assembly. You'll need a circlip tool. and you will get brake fluid everywhere, so empty the resevoir first. Then after you refill the fluids with DOT4 brake fluid, you have to bleed the darn thing at the transmission slave cylinder - with a vacuum bleeder (Mighty-Vac) or else by pumping the clutch pedal about a million times.
It's probably better to have an independent BMW shop do the job if you are not really into mechanics.