Date registered: Feb 2007
Vehicle: 03 E320 4M Wagon & 97 E320
Mentioned: 0 Post(s)
Quoted: 10 Post(s)
Your car could use either the old or new tensioner system, depending on your engine number.
12-072237 is the starting engine number for the new (much better) style. Hope it is because the old style is a real pain. If you have the new style, all you need to do is to use a 15 mm socket to turn the bolt at the center of the tensioner pulley CLOCKWISE to release the tension. You can find your engine number on your car's datacard or use your VIN to check.
If you have the old system, then I suggest you go to the W124 forum to do some search and reading. Be careful with it.