The 6.2L M156 in the 2007-2009 E63 is known for corroding/stretching head bolts, a several-thousand-dollar job commenters treat as inevitable on 07-09 cars, with ARP fastener sets recommended as a durable fix. Whether every car truly needs it is disputed: some owners report no failure at high mileage, and AMG reportedly characterized it as affecting only a small percentage.
M156 head-bolt corrosion and preventive replacement (E63)
Mercedes-Benz E55/E63 AMG (W211) · mechanical