I forgot about the other criteria for determining a worn out clutch. It is very specific to a Benz. There is a special tool that you can buy or make that is simply a u shaped piece of sheet metal that you slide into a slot at the slave cylinder. If the clutch face is worn beyond its limit, the gauge will bottom out on the slave cylinder shaft. If it is not worn, it will not go in all the way.

As I recall the 123 Haynes manual has dimensions for making this tool, or you can pick one up at the dealer for a couple of bucks.

Good luck,