A loss of braking efficency (low pedal & slight steering swerve when brake system responded to pedal travel) was diagnosed by the dealer as air in the brake system. No fluid leakage was evident, fluid level is correct, Pad wear minimal for the milage, and no root cause for the air infiltration was identified. The corrective action was to 'bleed the system'. This 2001 S80 T6 has 15,000 miles and I am concerned that a root cause for the problem was not found. Is there a history or recall on this or similar brake system problems?