Transfer case: pull the bottom plug with a 3/8 drive socket, let it drain into a bucket for about 10 minutes, then replace the bottom plug. Open the top plug, use some sort of tube attached to the fluid bottle to get it in the case. Fill to the recomendation in your owners manual with manual recomended fluid. Usually Mercron or Mercron V. Replace the plug, tighten it to snug. The plugs are supposed to be torqued but I never have torqued them in my life.
Diff: Buy a gasket, take the cover off, drain it into a bucket. Clean the gasket surfaces, Add the new gasket with RTV and replace the cover. Torque the bolts to spec, (22 in/lbs if I remember correctly), remove the plug with a 3/8 socket and fill with the fluid recommended in your owners manual through the plug until you can't get anymore in. Replace the plug and your done. If you have limited slip, you also need to add a bottle of friction modifier.
