Two problems related to seat belt have been reported for the 1998 Mercury Sable. The most recently reported issues are listed below.
Seat belt failed. Yh.
The failure of the five point harness (maker: costco, model: 20448bng, made: 03-03-00) fails in the regard that the chest clip is easily slid down by the child enabling them to free their arms. This creates enough slack in the straps that they can conceivably free their legs from the restraint and, indeed, their enire body.