Well, I will give it a try first, as this is what the parts man suggested also. I just wish I could get a better handle on how these viscous fan clutches are supposed to act under different conditions. I am having a similar problem on an old Dodge Motorhome with a 440 engine. I have already replaced everything on it. When its fan clutch engages, you can definiltely hear the increased "roar" of the fan blades. I hear nothing like this on the Mercedes. I saw the special tool in the manual, and they do not have it at the dealer, but it looks like I could make one out of a steel rod of some sort. It just holds the pulley so you can unscrew the center bolt, right? It is cramped up there though!
Thanks for the input!