Your first step in servicing or repairing the brake master cylinder is to drain and then remove it. After that, unscrew the brake master cylinder reservoir cap and transfer the fluid to a container. Hit each pin with a hammer and pin punch until the one securing the master cylinder to the brake master cylinder reservoir comes loose. Have the cylinder body held in a vice that uses brass jaws and use a pry tool to remove the brake master cylinder reservoir from the grommets. Rock the brake master cylinder reservoir gently to its side and pull it out of the grommets, then remove the old grommets from inside the cylinder. Make sure the friction points are clean, then install the new grommets in the cylinder, using only a straight push of the finger, nothing more. Insert the brake master cylinder reservoir into the grommets and push it back and forth while going down to make sure it's sitting perfectly. After that, fit the reservoir retaining pins into the cylinder body and bleed the master cylinder outside the car.