You really should get a manual, theres a lot of stuff that the tensioner is buried under and trying to tell someone in this forum would almost be impossible, the book will give you pictures, torque specs etc. I know the M.B. manual would be hard to get a hold of, but maybe the Haynes book?
If you can't find it, I would be happy to copy the procedure out of my 86 300E manual for you. The parts shop here may even have the CD by now? A purchase that you will use many times over.
See Ya, Chris