Sound like you need the fan clutch bearing bracket asembly. Go to FastLane and check your model for it under Cooling System.
If it's the same as on my 86 300E it's like the one pictured below.
It'll run you about $106 - $126. The inner bearing race
is the shaft that the fan clutch mounts on, so you can't just replace the bearing; you have to replace the whole assembly (just did it on mine a short time ago). While you're at it you might want to check or replace the accessory belt idler pulley (about $35) and the accessory belt tensioner ( $126 to $142 ) and the belt itself ($17). Check my post in this thread about tensioners to determine if your belt tensioner is good or not:
http://www.peachparts.com/shopforum/showthread.php?threadid=76303
Hope this helps,
Gary