Several posts here about mysterious failures of rear axle seals. My experience: Had a local mech try to adjust parking brake. He could not, put truck on lift, found some strange lubricant on the parking brake shoes - diff oil as it turned out. Took it to dealer who found that air vent on diff housing was blocked, blowing out the seals and destroying bearings. Fixed under extended warranty (2007 OR). From the other cases with similar effects, suspect the air vent in diff is prone to blockage.