Chrysler 2005 PT Cruiser - Manual (Page 292)

NOTE: If your vehicle is equipped with a manual
transaxle, the Brake Fluid Reservoir supplies fluid to both
the Brake System and the Clutch Release System. The
two systems are separated in the reservoir and a leak in
one system will not affect the other system. If the Brake
Fluid Reservoir is low, and the brake system does not
indicate any leaks or other problems, it may be a result of
a leak in the Hydraulic Clutch Release System. See your
local authorized dealer for service.
Use only manufacturers recommended brake fluid, refer
to Recommended Fluids, Lubricants and Genuine Parts
for correct fluid type.
Brake Fluid Master Cylinder
292 MAINTAINING YOUR VEHICLE