First, do a search on 'M103 serpentine belt.'

Here are the steps:

- detach fan shroud from radiator and rest over fan
- take an 8mm hex to the front of the fan and a 3mm allen key or similar size bent wire to the back of the fan at the 1 o'clock position to hold the fan to remove the fan and shroud
- loosen the 19mm head bolt at the 8 o'clock position of the power steering pulley. DO NOT remove the bolt. A full turn should do it
- loosen the 13mm hollow shaft positioned vertically behind the power steering pump
- the belt should be loose enough to remove. DO NOT remove the belt until you note how it is routed and/or have a diagram from the shop or owner's manual
- installation is the reverse of removal noting that there is a tension indicator above the 19mm head bolt. Tighten the 13mm hollow shaft until the pointer is at but not beyond the full left/CCW mark on the indicator

If the belt is loose even with the indicator reading proper tension, the tensioner should be replaced.

I don't know what the shock does. My old one was as stiff as the new one so I didn't replace it.

Put a sheet of cardboard over the radiator fins so you hurt yourself of the radiator if a tool slips.

Good luck.

Sixto
91 300SE
87 300SDL
81 300SD