Obtain a repair kit specifically for the brake master cylinder fitted to your car. With the brake master cylinder removed, brush and clean away all external dirt. If equipped with remote type servo units, withdraw the flexible bellows and push rod before extracting the circlip from its groove in the end of the cylinder body. Extract the internal components and keep them in strict sequence for refitting, noting that the design will vary according to the type of brake master cylinder. Wash all parts in hydraulic fluid or methylated spirit and examine the piston and cylinder bore surfaces for scratches, scoring, or bright wear areas; if any are observed, renew the brake master cylinder completely. If the components are in good order, discard the old seals and fit new ones from the repair kit, using fingers only to manipulate them into position. Dip the internal components in clean hydraulic fluid before installing them.