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Hello and welcome to just answer and allowing me to assist you. Well actually there is no procedure for flushing the gear oil from the differentials and transfer cases it's just a drain and fill. And if I may suggest to add an additive that would be very beneficial as well. Use either forte or wynns gear oil additive , both will raise the index number from 7 to about a 9 and also supply superior friction proofing.You will need new drain and filler plug washers and a siphon gun to put the new oil back in. Always undo the filler plug first just in case it seizes .Would you like some pics to help you?Would you like to talk on the phone so I can walk you through it?