DO NOT DO THIS ON A GTR BOX..... YOU WILL FILL THE TRANSFER CASE NOT THE GEARBOX!!!!!!!!!!!!!!!!
i had the same prob on my box the dickhead at the work the owner b4 me took it tighen them up way to much.... for the record.... its a plug that holds oil in the gearbox, its a tapered bolt... therefore it dosent need to be tighened up stupidly. just firm it up and than half a turn tight.... its not wheel nut.... or a dam rod bolt. its a just a plug.
ok i was able to undo my filler plug, lucky enough i have a 2post hoist in my garage so it was easyer to work on. for the drain plug this is where the real prob was, i had a rattle gun and all on it and there was no budging. So what i did in the end was, get a drill bit that fit the 1/2inch hole the break bar gose in, and drill it, DO NOT drill right throw, if you do u will break the magnet on the back and will go all over the box on the inside, as its magnetic... lol. Just lightly drill in 2mm-2.5mm and than little bits at a time, it will take the tension off the taper of the bolt/plug. it worked for me, i didnt think it would but after 4hours trying to get it out, it was my only option and it worked. just be careful.
hope this helped. : D