Hydraulic Leak Check
NOTE: There is a common clutch and brake fluid reservoir, therefore it is possible that a clutch leak can lead to reduction in the reservoir level.
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 the system, bleed then apply the brakes several times. Examine the system to verify that the reservoir fluid level is actually dropping. Locate and repair the external leak. If the fluid level drops and no external leak can be found, check for a brake master cylinder bore end seal leak.