Read the crankshaft balnce failure - I forgot as to whether this applies to this engine or not but other than that it has a very good reputation so far. Is it a 4Matic? Are you going through a dealer to get it?
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (194,000)
1999 E300 Turbodiesel (244,000 miles, dies at 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles)
2011 Audi A4 Avant (129,000 miles) hate this car!
BMW 330 xi 6 speed manual (100,034 miles)