As far as O2 sensor is concerned, it should be replaced every 60,000 miles. This is from my 95 E420 maintenance manual.
One tip: apply hot lubricate paste (MB part # 000 989 76 51) on thread of lamda sensor.
2005 Triumph Bonneville T100 (Black/white) [Sold]
2007 GL450 (Dersert Silver)
2009 Toyota Corolla (Metallic Silver)
2002 Tundra V8 - 2WD (Desert Sand)
1995 MB E420 (Silver Smoke) [crashed, now resting in peace at Silverstar Recycling Center]