One problem related to transmission not engage has been reported for the 1998 Mercury Sable. The most recently reported issues are listed below.
I drove the car to do errands and it was not having any problems. I parked the car at the mall and came back to drive home and the transmission failed. The gears would not engage. I was forced to have it towed home. It showed no signs of having a problem, and the transmission fluid was intact with no signs of a problem. This appeared to be a costly repair, so I chose not to fix it at this time.