My X-REAS failed on my 03 Limited at 138,000 km. There was a leak in the system - in the line behind the Driver’s Side Centre Control Absorber. Leak was likely caused by corrosion of the line due to road salt used up here during our Canadian winters.
Fluid that had dripped onto the driveway was the first indicator of some sort of problem. As more fluid leaked out of the system, the suspension became worse.
I removed the entire X-REAS system (too costly to replace), and installed the standard SR5 suspension (to keep it relatively stock).