1994 Buick Regal Owner's Manual - Page 230

Brakes Brake Master Cylinder Your brake master cylinder is here. It is filled with DOT-3 brake fluid. 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 work is 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 normal brake lining wear. When new linings are put in, the fluid level goes back up. The other reason is that fluid is leaking out of the brake system. If it is, you should have your brake system fixed, since a leak means When your brake fluid falls to a low level, your brake warning light will come on. See "Brake System Warning Light" in the Index. 228