Typically the Brake Master Cylinder may be of a composite type containing the reservoir or may contain separate reservoirs for each circuit, its construction however is the same. Before removing the Brake Master Cylinder, the connected plug, the fluid level sensor, hydraulic brake lines should be disconnected and the ends covered to avoid the loss of the fluid and prevent dirt from getting into the hydraulic Brake Master Cylinder as the fluid strips the paint from the body work. Remove the mounting nuts and, without affecting the hydraulic circuit rigid pipelines, get the Brake Master Cylinder off the servo unit. Remove it once and then remove the hydraulic fluid, wash the exterior gunk and then place the Brake Master Cylinder with the piston stop bolt standing up in a vise with soft jaws. Shake off the dust excluding boot, use a screwdriver to put pressure on the primary piston so as to relieve pressure in the secondary piston, and then tighten and remove the stop bolt. Push out the circlip so the primary piston, secondary piston, and the return spring may be thrown out without the need to disconnect the primary piston spring or the seals from the pistons. Check the pistons and cylinder bore for scoring or metal to metal rubbing; then the Brake Master Cylinder should be replaced in full. If so, the components should be washed using clean hydraulic fluid or methylated spirit, the valve cases should then be unscrewed to remove the check valve as well as the spring; which should also be cleaned before being re-fitted. Get an assembled repair kit which includes new primary and secondary pistons with new spring seals pre-fitted on them. Coat the secondary piston and spring with rubber grease or clean hydraulic fluid before installation and do the same for the primary piston/spring assembly before snapping on the circlip. Smash with a screwdriver the initially situated piston into the cylinder completely, fix its position as well as screw the stop bolt of the second piston and properly slot the dust excluder. Before fitting the Brake Master Cylinder, check the servo pushrod to primary piston clearance; reconnect the pipelines, reservoir hoses, and the hydraulic fluid supply reservoirs, then bleed both hydraulic circuits and reconnect the fluid level sensor plug.