Two problems related to seat belt have been reported for the 1998 Lexus ES300. The most recently reported issues are listed below.
Both left and right rear seat belt buckles have failed. I am unable to insert belts into the buckle. Cleaning and lube had no affect.
Seat belt retraction failure. The seat belt on my 1998 Lexus had been slow to retract, sometimes not retract at all. It appears this problem is not unique to this model or year. Many other vehicles made by Toyota and Lexus have the exact sam problem (based on searching on the internet). This is probably due to a defect in components of the seat belt assembly.