1999 Ford F-150 drivetrain & axles problems

My son was driving his 99 f150 southbound on a two lane highway, going about 50 MPH when he heard a pop, and then the truck went out of control. The rear of the pickup began to travel left across the highway. In the northbound lane, it began to roll over, drivers side first, finally landing upright at the left edge of the highway, then slid down an embankment front first in some trees. The left rear axle had fractured and snapped and the hub and wheel had come off.

A high pitch noise coming from rear axle assembly and subsequent failure of the entire rear axle assembly. Dealer mechanics have found foreign components inside the rear differential assembly (a silicon sealer squeezed and wedged between the ring pinion gears and the input shaft) that may have caused the problem. They found the rear axle lubricant to be burnt and metal debris was also found inside the casing of the differential assembly. Vehicle failed at around 55,000 miles and 6 years of service.