1998 GMC Safari Owner's Manual - Page 294

There are only two reasons the brake fluid level why in the reservoir might go down. The firstthat the brake is fluid goes down to an acceptable level during normal brake liningwear. When new linings are put the fluid in, level goes back up. The other reason fluidis is that leaking outof the brake system.If it is, you should have your brake system fixed, since leak means that sooner a or later your brakes won't work well, or work won't at all. So, it isn't a good idea to "top off' your brake fluid. Adding brake fluid won't correctleak. If you add fluid a when your linings are worn, then you'll have much too fluid when you get new brake linings. You should add (or remove) brake fluid, as necessary, only work is when done on the brake hydraulic system. 63 12