One problem related to power assist brake hoses, lines/piping, and fittings has been reported for the 1997 Mercury Grand Marquis. The most recently reported issues are listed below.
1. Car was being driven at normal speed, approximately 30 mph, and brakes were applied. Brake pedal traveled further than normal and brake warning light illuminated. When I arrived home I opened the hood and saw the brake fluid level in the master cylinder had dropped significantly. On further inspection I saw brake fluid on the frame rail on the driver side of the car at a location under the driver side front door (approximately). 2. It appears that the rear brake line was rubbing on the car body/frame structure and wore through allowing the brake fluid to leak out. 3. No repairs have been done yet. I am still investigating my options: repair at my expense, file a claim with Ford, etc.