Leak Checks
It is possible that all evidence of fluid leakage may have washed off if the vehicle has been operated in rain or snow, as brake fluid is water-soluble.^ Refill brake master cylinder reservoir and bleed system.
^ Apply the brakes several times.
^ Examine the system to verify that the brake master cylinder reservoir fluid level is actually dropping.
^ Locate and correct the external leak. Check all hoses, lines, calipers and master cylinder for signs of leakage.
^ If fluid level drops and no external leak can be found, check for a brake master cylinder bore end seal leak. Testing and Inspection