Hub Contamination
WARNING: This page is about a different car, the 2004 Ford Pickup, 2004 Ford F550 Super Duty, 2004 Ford F450 Super Duty, 2004 Ford Excursion, and 2004 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
If contamination (water, mud, etc.) is found in the hub cavity, look for the source. If it is due to system leaks other than the hub lock, they must be found and repaired. Always install a new hub lock O-ring before re-use.