Brush off any dirt from the differential inspection cover area, remove bolts, and let fluid drain into pan as cover comes loose. Remove any gasket material, whether fiber or RTV type from cover and mating surfaces, and otherwise clean the cover. Replace with fresh gasket in place, or using RTV per instructions on product tube. Get all bolts started to thread before tightening any all the way down. Remove fill plug from cover, and fill with GL-5 75W-90 Gear Lube until it starts to come back out of the hole while vehicle is sitting level, and replace plug. Should take about 2 and 1/2 quarts.
All of the above is assuming a 1500 1/2 ton model, without Posi.
