Over a year ago I purchased an 81 240d manual. I bought it from a repair shop who had reciepts of alot of stuff done on it including a new clutch. Not more than three weeks later I pushed in the clutch while driving to find it not there and fell to the floor so to speak. Later I found out that everytime i pushed in the clutch...it would spit a little bit of brake fluid from the slave cylinder. It was easy to replace and it only cost me 30 or 40 bucks at Inter Auto Parts in San Diego. I would think that if you plan on replacing the clutch than I would also plan on replacing the slave cylinder. Unscrew a couple bolts like 12mm and the oil line, to attach do the reverse. With mine I just got in the cab and pumped the clutch about a 100 times and I had a new slave cylinder. I have heard of some guys that do it differently but it worked for me.
-Stephen