The 722.6 five-speed automatic (E55) is regarded as extremely strong, said to handle 800+ hp with regular fluid and supercharger-oil service, though some cars are known for a transmission rebuild around 120k miles if neglected. Recommended intervals cited include 50k trans flushes and supercharger oil and cooling-system service every 50k.
722.6 transmission durability and service intervals
Mercedes-Benz E55/E63 AMG (W211) · mechanical