I agree. dollars to doughnuts its the top bushing on the little shock absorber on the belt tensioner. It attaches right behind the thermostat. A bit of a job to get out as the fan, three pulleys and the tensioner has to come out to get to it. I know as I just did this repair 2 weeks ago on my 300sl. (104). If you need more info let me know and I'll walk you through it. You'll need a torque wrench, something to hold the pulleys (strap wrench works) and some high-temp sealer for the one "wet" hole that you need to extract a bolt from. I couldn't be bothered to chase down a bushing so I just replaced the whole shock (accessory belt tension damper) 31.94 @ importpartsonline.com