mad_machine wrote:
I once replaced a transmission and only discovered after it was in that the fill plug was completely boogered up and would not accept the proper sized allen key. I ran a small diameter hose down to the vent and did an "IV drip" overnight to fill it with fluid
if all else fails i would definitely consider this as an option. How often do you change rear end fluid? with how long the intervals are it may be worth the time it takes to fill though the vent rather then continuing the fight with the fill plug.
and good on ya for trying to get the fill plug out before draining 
if it's like any diff with a bolt on cover, go to the store and get a drain/fill plug kit and install the plug into the cover at the same level as the stuck plug in the case. no more worries about the stuck plug.
It's not a cover. The housing is one piece and the third member bolts in from the front. I'm going to give it one more try by reshaping the plug to get a good grip and if that fails to produce movement I'm filling through the vent. I really don't like not having a way to check the fluid level but to be completely honest I haven't checked the level....ever, so I suppose I should just relax about it.
Filled with the proper amount of fluid through the vent on top of the differential. With the plug stuck I don't have a way to check fluid level, which to be honest I haven't done since we bought it, so I'm no worse than I was before other than knowing about it. At least it doesn't leak.
Thanks for all of the suggestions. Someday something will break back there and I'll fix it all in one go.
Does it have a limited slip? What kind of oil did you use?
It has the factory Toyota E-locker. Fluid used was Royal Purple 75-90.
I broke loose the plugs on the transfer case and transmission. Both fill plugs had been tightened to "tight enough the wrench slips and rounds the head". Drain plugs all around were proper torque and easy to open. I hate PO's so much.
In reply to mazdeuce:
But you can save $5 on crush washers if you crank down the old ones until they quit leaking.
I know you've already finished, but It was mentioned earlier about torching the thing and applying candle wax. I just wanted to say that I saw that on YouTube and it worked to get a broken exhaust stud unstuck for me that torching and penetrating oil could not.
