Your MB has one of the world's best diesel engines. They are used in "Hamburg Taxis" and many of them achieve 1,000,000 kms with only routine servicing. The engine's camshafts are turned over by a high class chain and sophisticated oil tensioner/damper system. The camshafts are responsible for opening and closing the valves that let in the fuel/air mix (inlet valves) which goes out burnt through the exhaust valves. Many people will say that cam belts are quieter but in the case of Mercedes, BMW, Toyota and Honda sound (good) engineering will result in less noise.
Ford uses a chain system in its new high performance 1.4 petrol unit and you can see the chain on the front of the engine.
This is one of the new very high compression petrol engines that is replacing diesel ones and will be just as economical. PSA (Peugeot/Citroën) are now buying petrol engines from BMW whilst Renault already has its excellent and highly efficient TCE petrol engine range. The 1.4 is a little gem.
The chain for the cam shafts is driven by the big pulley (wheel) which is on the bottom of the engine (with red disc) and the chain goes up to the two smaller pulleys on the top.
It won't be long before France can breathe more easily! Incidentally as I frequently tell my engineering students, "Very rarely will you find a belt driven cam in a marine diesel engine!!! Why?"