Master Cylinder: Disassembly

Remove mud and dirt from the surface of brake master cylinder.
Secure the master cylinder on a vise.
Remove the pin which secures reservoir tank to master cylinder, and then remove the reservoir tank and grommet.
Remove the cylinder pin with magnetic pick-up tool while pushing in primary piston by screwdriver which wrapped with tape.

Fig 1: Removing Cylinder Pin
Courtesy of SUBARU OF AMERICA, INC.
Remove the C-ring. (With VDC)

Fig 2: Removing C-Ring (With VDC)
Courtesy of SUBARU OF AMERICA, INC.
Pry up the pawl and remove piston retainer. Hold piston retainer tight, because the piston may jump out from master cylinder.

Fig 3: Prying Up Pawl
Courtesy of SUBARU OF AMERICA, INC.
Extract the primary piston assembly and secondary piston assembly straight out, while taking care not to scratch the inner surface of cylinder.
Use brake fluid to wash the inside wall of cylinder, and piston assembly. If any damage, deformation, wear, rust, and other faults are found, replace the faulty part.