One problem related to brake master cylinder has been reported for the 1998 Buick Lesabre. The most recently reported issues are listed below.
While driving about 55 mph rear wheels on the driver's side locked up for no apparent reason. Vehicle veered off the road and back on. Everything seemed to be okay. About a half an hour later, this happened again. Vehicle was towed to a dealership. Dealer was not able to find out what caused this problem. Also, master cylinders were changed on both rear brakes on June 3, 2000. Owner not sure if this could have caused the wheel to lock up. When the vehicle jerked sliding to the left, the wheel rim of driver side became bent locking it against the wheel bracket.