What part in the master cylinder helps keep air from contacting the brake fluid yet allows the fluid level to drop as the disc brakes wear?

Question

Quizplus · Accepted Answer

The rubber diaphragm or floating disc in the master cylinder is designed to flex and move down as the brake fluid level drops (due to brake pad wear), while simultaneously preventing air from entering the system and contaminating the brake fluid.

What Part in the Master Cylinder Helps Keep Air from Contacting