Well, have you checked the fluid and bled it yet? Have you looked into the slave cylinder?
Do that first. Start with the DIY things that are cheap/free. Check fluid. If it's low, top it off. Bleed the system. See if that improves things. If it does, you know it was just low/had air bubbles.
If it was low, start looking for leaks. Check the lines and the cylinders. If all is good, consider that perhaps it just needed to be topped up. If the problem returns, you should have a mechanic properly diagnose the leak.
If that doesn't work, there could be other problems with the M or S cylinders. This is getting out of my territory, though.
And to me, that does not sound like a pressure plate problem. Like I said, start with the small stuff. I have yet to have a dealer suggest an easy fix, even when that is all the problem requires.
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