Well he's right about that being a way to see if they are worn out, but completely clueless about why its shot and how it works. Some movement is normal though.

The clutch like material he found is just that, an overtorque prevention slip clutch. Its tensioned by belleville springs (washer like things). It is normally locked and has nothing to do with the flywheel turning a little back and forth. It will slip if overloaded to "protect" the flywheel or transmission. Supposedly it can over heat in certain situations (like when doing tight maneuvers with a heavy trailer). I'm not sure exactly how much its designed to slip, but after doing it a bit, it will wear out and slip when your truck is unloaded and going up a steep hill (because mine did and it sucked!!)

The plastic things that hold the springs in place will frequently wear down, or crack and break (like in the pictures). I had at least one that was completely broken off and one of the springs had been rattling around some, thats bad too. My guess is that the springs will fatigue over time and become a little shorter and that with wear on the plastic parts causes the excessive movement.

Also, a DMF can be taken apart with drilling out the rivets. It takes a couple screwdrivers to pry out the springs. Putting it back together like that is a pain in the ***, but doable.