This is not the easiest idea... but would work for now.

1. Take off the wheels.
2. Remove 4 bolts holding in each axle.
3. Slide inner axles out about 2" or so (support them to prevent seal damage, or just pull them out all the way)
4. Unbolt diff.
5. Oil will drain, clean it all out.
6. Reverse steps.
7. Fill through breather.

I realize labor intensive, but it's not like you have to do this every week and you wouldn't risk breaking or damaging the drain bolt to the point you couldn't get it back in. Would be a bummer to end up with a leaky diff if your drain bolt removal attempts cause something to fail.

Actually... don't some intentionally weld or shave off the drain bolt? I think they replace a few of the diff studs with bolts and drain that way. Maybe others with more knowledge will chime in on this method.

 

His drain plug comes out fine... it's his fill plug that's stuck.

 

Oh...sorry. That's what I get for posting too late at night.

 

If it's just the fill plug, why not just drill / tap a new one?

 

Here's an idea, drill a hole in the fill plug and tap it for a plug, like maybe about 3/8" NPT. You'd have to wash out the metal shavings though. Or drill out the fill plug until you can get a big easyout in there. You'd need a big easyout though, a small one would break too easy.

 

Not if it's actually welded - you'll have to grind the head off, then MAYBE you can spin what's left out of the housing.

I think it's an M18 tap...