If the nipple is nor in fact at the top of the slave cylinder. By design it is to bled by displacement by the fluid being charged into the system. Any air will stay ahead of the fluid due to the much higher Denstity of the fluid. I cannot visualise and place in that simple system that could hold air in the presence of fluid. I see a simple reason that the master cylinder appears to be a resupply system.Where functionally it is anything but on any master clutch cylinder with a pushrod installed that is long enough to make the piston cover the top port.

Again I refer to the production line for the car originally. There is no time for the factory installer of the clutch fluid to fool around as so many members have landed up doing. If the input port is not covered this should be the easiest job pretty much on the car in some ways.

You bleed to get air out. Where it should be automatically displaced in that setup. You also really cannot bleed a closed system. Especially if there is no provision to do so. That is definatly the case with the clutch hydralic setup. There is just nowhere to hold air as the fluid level rises on bottom fiiling.. There also may be a slight design issue with the master cylinder. Or in an old master a swollen rubber cup in there.

Bear with me that I never before considered any issues. Of why so many people where having issues filling that very simple system with fluid.If one wants to pre prime the slave cylinder. You would press the piston in and hold it. Add fluid to it. Then as you held the slave with the opening as high as practical. Probably required to fill it anyways. As the piston came back it would push the fluid out with the air leaving first as it is on top of the fluid.

Stoking it or pumping it will not get any air out. Unless you are adding fluid during the process. when I seem to make no sense. I have no issue with it being discussed. Usually by the time it is hashed over. People have gained an understanding or insite they may not have aquired or considered otherwise.

We have some questionable termanology in play for the clutch hydralic set up as well. The bleeder on the slave cylinder is not the bleeder. It is the filling device. The system bleeder must be at the highest point in this system where air will arrive at. That is the exit port of the master. There is nowhere else it can get trapped. Other than just below that exit port. You are going to be in a world of suffering if that exit port is sealed. Sometimes things are so simple there seems no need to understand them.

Also be kind as my eighty year old brain in a few months. Is not what it once was perhaps. I do not profess to be right. I do like to make people consider things. I can be wrong and take no offence in it being mentioned. People that have no tollerance tend to have locked minds. My way or the highway has no appeal to me. Perhaps the simplest test to establish if that exit point on the clutch master cylinder is open. If the line to the slave cylinder is not connected or the bleeder is open. Fluid should flow by gravity out that line. In enough quantity to indicate the master cylinder is involved in providing the supply. If it does not pass that test. Pull the clutch master cylinders push rod and test again. Beats tearing you hair out trying to make it work. Unless you are bald.
If that fill port was not closing off. You could let the clutch system just gravity fill. Any air would just find its way back to the master brake cylinder. Air would be slow moving upward though. I also think by simply opening the bleeder on the slave it would also simply gravity fill with no air in that system.

The more I think about this. Mercedes may have by design intended the exit or entrance point to the master clutch cylinder quantified by the application being used. To be closed off when the pushrod is installed. The why would be simple. Brake fluid is so hydroscopic. If the primary fluid in the master gets into the clutch hydralic system. We should be seeing more failure rates than we are. The pushrod may just be longer than required by either design or accident. I almost dislike it when an issue stimulates me.