The M103 engine is unlike most of the other MB engines as far as timing chain life expectancy goes. These are simple chains with only the crankshaft and camshaft sprockets to deal with. Add to that the fact that this engine has a ratcheting tensioner and you have the engine in the MB stable with the best timing chain record.
I am not saying this to discourage you from replacing the chain for preventive maintenance reasons, but unless your car has not had frequent oil changes, I really think you could run it a little longer. My 300E has almost 200k miles with the original chain.
The engines that really require "take no chances" timing chain management are the V8's.