******There was a thread a while back concerning depressing the clutch pedal which stayed on the floor. I had new master and slave cylinders fitted which did not solve it******

I had the same symptoms and it ended up being the clutch master cylinder. I thought it was odd because it had just been replaced in the last 10K miles. While removing the cylinder, I also snapped the metal fluid line that runs between it and the slave cylinder - oh FUN! When I finally received that part and bent it to shape, it worked once everything was installed. I wouldn't want to learn that all over again. Having done it now, it seems pretty simple but god I hated it at the time. I saved $165 labor and learned something very useful about my 635!
Chris '85 635
Columbia, SC