- :
- State of Jefferson
- :
- 2017 CX-5 GT AWD+
The fluid level in the master cylinder goes down over time because pad wear allows the caliper pistons to move further inward, pulling fluid from the reservoir.
But only if an equal volume of air enters the reservoir. Otherwise there'd be a vacuum and it couldn't draw-down the brake fluid.
Both right, so you can be sure that it's not sealed. Otherwise water wouldn't get into it, either.