"Clicking" clutch pedal
I can think of a number of things that may cause the noise you describe. Most of which are easily corrected with appropriate lubrication. Given the minimal amount of detail you provided, it is somewhat difficult to diagnosis your problem, but here goes.
First, is the clicking heard from inside the cabin? Stick your nose near the pedal assembly to determine if the noise is not simply something striking the pedal assembly (like a loose wire loom.) Next, rule out the possibility that the pedal assembly is simply in need of lubrication. Again, is the sound coming from that area?
The more likely scenario is a lack of grease on the throwout release bearing lever where it is contacted by the slave cylinder piston. Others may have a better name for this piece. This assumes you are still using the Getrag 4 speed transmission that was standard fare for the CSI's.
You will need to get under the car for this procedure. If you locate the slave cylinder attached to the bell housing, look carefully and you will notice how the hydraulic cylinder moves into the arm of which I spoke. It is this lever which causes the clutch to be released. I suspect that where the slave cylinder piston mates with that lever needs some grease. Application is fairly self evident and simple wheel bearing grease should do the trick.
I believe most Coupe clutches were equipped with a plastic cup grease reservoir and retaining spring. Over the years, most cars have lost said reservoir. I know mine have. Since you mentioned recently replacing the slave, it is possible the piston was installed dry or with only a too-light coating of grease.
Beyond the above suggestions, I think the remedies are far more involved. Issues from sticking throwout bearings, bad pilot bearings, loose bell housing bolts, loose master cylinder retaining bolts, loose master cylinder linkage and broken clutch plate spring(s) could all cause clicking in one form or another.
I do not believe the following diagrams are the most helpful, but maybe you can find some benefit from them.
See diagram 21/3 as a possible aide
http://www.realoem.com/bmw/partgrp.do?model=7031&mospid=47808&hg=21&fg=05
See No. 4 the far right area of the piston for grease
http://www.realoem.com/bmw/showparts.do?model=7031&mospid=47808&btnr=21_0114&hg=21&fg=10
Good luck and keep us posted.
