I have an 85 635csi that I've had since 86. I've also got a clutch problem that I can't figure out. The hose from brake resevoir come loose and drained the system. I repaired that and refilled it. I bled (a lot) air from the system and got a good clutch. Now I can drive it for a while and the clutch goes completely away. Let it sit 5 minutes, give it a couple of pumps, and I have a really good pedal again! I'm stumped. The line from the clutch master to the slave seems to be in good condition. Does anyone have any ideas?

You probably still have air in the slave cylinder unless you removed the slave and then pushed the push rod all the way in and then released it slowly. This procedure is mentioned in the Bentley manual.