The brake fluid reservoir on a 1987 Buick Regal is typically located
under the hood, near the master cylinder. The master cylinder is the main brake component that distributes brake fluid to the wheels. The reservoir is usually a small, clear or translucent container with a cap. It may be labeled "Brake Fluid" or have a brake system symbol on it.
However, always consult your owner's manual for the precise location. The manual will have diagrams and specific instructions. Using the wrong location could lead to serious problems.