Your engine has a double row timing chain as opposed to the M103 which has a single row chain. The double row chain is extremely durable and can go much longer than the single row chain. If it makes you feel comfortable you can replace the chain at around 100k. This seems to be the popular concenus among MB owners though no specific recommendation is made by MB.
It is possible that you have a hydraulic element bleeding down after the engine has been shut off for awhile.
Timing chains will eventually stretch no matter how often you change the oil. Its a law of pyhsics. Apply heat to metal, the metal expands. Timing chain rattle occurs for one of three reasons; a) A guide has broken allowing the chain to slap, b) The tensioner has failed and bleeds down when the engine is shut off, c) The chain has stretched beyond the limits that the tensioner has to keep proper tension on the chain.