Okay here is my take on changing the differential lube as I just got done doing it. Jack the wheeler off the ground...on the front take out the bottom plug and start draining. Take out the fluid level plug just below the fill plug 6mm. I blew air into it to try and get every drop out of it. Put the drain plug back in. Now take out the fill plug and using the gear lube pump on the bottle (a plastic pump with a hose on it to fill in tight places) start filling it up as you turn the wheel next to you for faster displacement. I basically filled it to the top of the fill hole and let the fluid level hole drain it out to the proper level. After it's finished draining put the plugs in.
Do the same for the back Diff, but it doesn't have a fluid level hole. Fill it up while spinning the wheel, let it level off on it's own and make sure it is level with the threads of the fill hole, if not spin the wheel and do it again until it levels off flush with the threads then put the plug in. The back diff seems to take a bit more than the front (maybe just me), but a quart will more than do it. Little messy, but no more than changing the oil in it. Hope this helps!!