Release the parking brake and raise the rear of the vehicle, supporting it securely on jackstands while blocking the front wheels. Remove the wheel and brake drum, and if equipped with ABS, take out the ABS sensor. Next, remove the brake assembly and disconnect the parking brake cable along with the hydraulic brake line to the wheel cylinder. Detach the four backing plate mounting nuts to free the axleshaft from the rear axle housing, then carefully pull the axleshaft out, taking care not to damage the oil seal. Remove the O-ring from the rear axle housing, discarding the old one and preparing to install a new one. Use a seal removal tool or a big screwdriver to extract the old axleshaft oil seal from the axle housing, and then drive a new seal into the end of the axle tube, coating the lip with clean oil or multi-purpose grease. Install a new axle housing O-ring with a light coat of oil, ensuring the axleshaft is clean and free of burrs or metal splinters. Lightly coat the axleshaft with clean oil before inserting it into the axle housing, ensuring the splined inner end does not damage the new seal. Finally, reassemble by reversing the removal steps and tightening the four backing plate mounting nuts.