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The bottom picture IS the slave cylinder. It's piston rod pushes against the throw-out lever. That white plastic thing is like a ball & socket to push the lever. Have someone work the clutch pedal while you watch the lever...

Some cars have a big rubber bellows over that, but some don't. Try greasing it. That silicone spray goes away after a day or so (as you discovered).

If that doesn't do it, there's other possibilities that take much more work. Worst I suppose is the throw-out fork's pivot. You can't really reach it from outside...