The rear subframe is a documented weak point, particularly on northern cars, with a widely referenced Mercedes warranty extension (cited as 20 years / unlimited miles) covering the repair on many 2009-2016 W/S212 cars. Uncovered, replacement is quoted around $5,000, and the underlying safety concern is deteriorating bolts.
Rear subframe corrosion and warranty extension
Mercedes-Benz E63 AMG (W212) · ownership