One problem related to differential unit has been reported for the 1996 Mercury Sable. The most recently reported issues are listed below.
Transmission leaked fluid. Found crack in housing, caused by differential breaking down internally. Vehicle is just past 36,000 mile warranty. 2 days of labor and $1600 estimated repair for differential and transmission housing. Need to check if related to current "roll pin" transmission safety recall for 1996 Sable.