1995 Pontiac Bonneville Owner's Manual - Page 240

Brakes Brake Master Cylinder Your brake master cylinder is here. It is filled with DOT-3 brake fluid. fluid is leaking out of the brake system. If it is, you should have your brake system fixed, since a leak means that sooner or later your brakes won't work well, or won't work at all. So, it isn't a good idea to "top off' your brake fluid. Adding brake fluid won't correct a leak. If you add fluid when your linings are worn, then you'll have too much fluid when you get new brake linings. You should add (or remove) brake fluid, as necessary, only when workis done on the brake hydraulic system. There are only two reasons why the brake fluid level in your master cylinder might go down. The first is that the brake fluid goes down to an acceptable level during noma1 brake lining wear. When new linings are put in, the fluid level goes back up. The other reason is that When your brake fluid falls to a low level, your brake warning light will come on. A chime will sound if you try to drive with this warning light on. See '* ' B System Warning Light" in the Index. 6-27