Pontiac 2007 G5 Owner's Manual page 299

There are only two reasons why the brake fluid
level in the reservoir 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 and/or
clutch hydraulic system. If it is, you should have
the brake and/or clutch system fixed, since a leak
means that sooner or later the brakes and/or clutch
will not work well, or will not work at all.
So, it is not a good idea to top off the brake/clutch
fluid. Adding fluid will not correct a leak. If you
add fluid when the brake linings are worn, you
will have too much fluid when you get new brake
linings. You should add or remove fluid, as
necessary, only when work is done on the
brake/clutch hydraulic system.
CAUTION:
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If your vehicle has too much brake fluid, it
can spill on the engine. The fluid will burn
if the engine is hot enough. You or others
could be burned, and your vehicle could
be damaged. Add brake fluid only when
work is done on the brake and/or clutch
hydraulic system.
When the brake fluid falls to a low level, the brake
warning light will come on. See Brake System
Warning Light on page 165.
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