One problem related to power assist brake has been reported for the 1999 Chevrolet Malibu. The most recently reported issues are listed below.
I actually have two Malibus - one a 1998, the other a 1999. Both have self-adjusting rear drum brakes which do not self-adjust, resulting in the front brakes (disc) doing all the stopping and overheating as a result. This causes rotors to warp, wheels to "shimmy" when brakes are applied, and loss of control of the vehicle in critical stopping situations at high speed. Request that you subpeona all gm service records for brake service on Malibus and see if there isn't a serious problem with repeated front disc brakes having to be replaced at frequent intervals.