One problem related to frame and members has been reported for the 1998 Jaguar XJ. The most recently reported issues are listed below.
Vehicle inspected by forest flock, motor vehicle forensic service. Found design flaw in front and rear sub-frame. Resulting in oscillation from front to rear of vehicle. Oscillation occurs from 50 mph to 80 mph during test. Mr. Flock states this will eventually lead to componet failure supporting engine and all components the sub-frames .