One problem related to differential unit has been reported for the 1999 Mercury Cougar. The most recently reported issues are listed below.
21,210 miles-brake rotor and pad failure,sunroof inoperable,passenger window inoperable-warranty 47,823 miles-complete charging system failure-warranty trunk has never opened correctly from inside-no solution 87,000 miles- starter motor failed-$250 91,519 miles-2 radiator hoses failed-$240 93,000 miles-manual transmission failed, differential gears -$2440 now I am having problems with my fuel pump. Throughout the life of this car there have been numerous problems cars don't receive until after 100,000 miles. In my eyes, it is simply a 100,000 mile lemon!.