How do you get into the rear head rest? Acts like I have a loose connection on one side. Works sometimes not others. Thanks, Garry

I assume you have the electric head rest, that is adjustable from each door and the switch on the dash. They are controlled by two modules under the rear seat, there is also a sensing circuit that tells the motors when to stop much like a window, one of my gears is stripped and it begins to ratchet.
As to your problem, my guys at MB talked me out of chasing it, but here goes.
the first step is to take out the seat bottom, disconnecting the heaters. then both pillar claddings on each side come out, and the package tray panels come out, they tell me the fasteners will become evident since the motors are bolted to the seat back. The package tray moves with the seat and is attaced to it. If you are intermittent it could be the modules, try the door controls, it will help you narrow it down, since those buttons adjust not just elevate and retract the headrests as the dash switch does. I retracted mine and leave them be!

I went outside and messed with it again. Found out that if I lean the rear seat forward, both sides work ok. Thanks, would not have even thought to do it if you hadn't mentioned the back door switches.