I simply do not believe their diagnosis as the phenomena of filings causing the issue makes no sense whatsoever in the context of their Report.
One would assume such a presence would signify a fault & the unit would be replaced whilst the other 3 ABS units would be inspected to confirm your braking system is perfect.
Erasing a Fault code is secondary, evidence of metal particles in the Brake System is the Primary fault that every other Dealer would resolve themselves.
Tel