I agree with Steve is a DYI job relative easy to do I recently change the belt, belt tensioner, tensioner shock, on my 95 E 320.

It sounds like your tensioner is bad so probably the belt is loose and easy to pull out. Take the fan cover/shroud out, if the belt is in bad shape just simply cut it and pull it out, if not then loosen the belt tensioner adjusting bolt, and pull the belt, take off the three bolts holding the fan blades (more room to work), take off the main bolt that holds the tensioner to the engine frame, pull the tensioner out, take off the tensioner shock, replace with new parts. You may want to consider while you are at it putting a new belt, and new tensioner shock, they are not that expensive, and you can always keep the old belt if still in good shape as a spare in the trunk of your car. You will need Metric tools, a set of Open Ended wrenches, Allen wrenches or Allen bids, and a decent Torque wrench. I used Loctite fastener (red label) on all the screws and bolts when I was putting things back together just to make sure nothing can work itself loose with the vibration of the engine. I wish I could show some of the pictures of the job I did but I have not been able to reduce the files enough so that I can post them in this forum.

My suggestion would be to contact Phil from Fastlane (the forum sponsors) that's where I got my parts at a very reasonable price. And you are right the prices from the dealer tend to be more, but if you look around you can get better deals. By the way, as reference material I bought both the Bentley manual (for my car) and the CD’s use by the Mercedes technicians they come very handy. Good luck

Bluerio

PS>> search the forum, there are many threads on this subject