The minimum replacement seems to be the Chain itself, the large Chain Rail and the Tensioner Spring. (Replacing the larger Chain Rail requires that the lower Pin be removed and on the Turbo Models I believe you need to remove the Crankeshaft Damper to do that. A good time to replace a leaking Front Cranshaft Seal if You have that problem.)
It is a real good idea to replace the larg Tensioner Chain Rail because you don't want the New Chain trying to ride in the ruts the old Chain wore into the old Chain Rail.
Some people also replace the other small Rails as they are Cheap.
You should certinly inspect the Camshaft Drive Gear but the Manual offers no specs or pics to help you there.
The Crankshaft Gear is the one that does the most work but most people don't seem to inspect that or replace it.
In fact if you replace all the Gears and the Rails you are getting close to $500 in parts.
Thread on Timing Chain and Rail Has list of parts
Recommended Timing chain brand?? - Page 2 - Benzworld.org - Mercedes-Benz Discussion Forum