One problem related to brake disc rotor has been reported for the 1998 Mercury Marquis. The most recently reported issues are listed below.
Rear brakes did not match. While traveling at 35-50 mph driver applied the brakes and brake pedal was hard. Driver heard a grinding noise in the rear. Took vehicle to a mechanic, and mechanic replaced 2 rear rotors and 2 rear brake pads. Also mechanic determined the right rear brakes had a different braking system than the left.