The coolant expansion tank is a known F90 weak point with an open BMW recall; failures commonly occur around 25k miles, and BMW extended coverage to 15 years/150,000 miles.
Coolant Expansion Tank Recall
BMW F90 M5 · mechanical
The coolant expansion tank is a known F90 weak point with an open BMW recall; failures commonly occur around 25k miles, and BMW extended coverage to 15 years/150,000 miles.