Originally Posted by CharlieVT
Do I understand correctly the internal hex of the filler plug is stripped and the hex wrench won't bite?
Put a penetrating oil liberally around the plug, repeat this a couple times and wait over night.
That will have little to no hope of working. The crush washer is actually a seal, and nothing will penetrate to the threads.
Go to an autoparts store and get a little tube of valve lapping compound.
Heat the final drive casing with a heat gun in the vicinity of the filler plug.
Put valve lapping compound into the internal hex of the filler plug, then insert the hex driver. Tap it in to be sure it is fully seated. The valve lapping compound may give enough "bite" to allow you to turn the plug. An impact driver may give better results than a hand wrench.
That is a good thing to try. It works quite well on stripped Phillips head screws
If this doesn't work, get a dremel tool with a cutting disk and cut a slot in the head of the plug. What you are making is a slot in the plug that will make the head of the plug like a big slotted screw. If you find a suitable flat, thin metal bar to use as a lever, cut the groove in the plug to receive the bar.
May work, but if the hex wrench stripped out, it is pretty unlikely that a screwdriver slow will work, unless it is wide enough to accept a pretty strong heat treated bar.
I would not cut off the head of the plug, that is likely to make matters worse.
That would be true if it were a corroded or galled bolt, but it is actually a really good way to remove things like this fill plug that are too tight, but not corroded or galled, which the fill plug is almost guaranteed not to be. It is a plated steel plug, in aluminum, and oil coated. Once the head is ground off, the plug will screw out easily. It might not have to be ground entirely off, just down far enough to get the clamping force of the head to the housing releived.
You could drill a hole in the plug and use an "easy out" but I would make this a last resort. You will get metal shavings into the final drive and will want to flush them out. Good luck.
I meant to use an EZ out in the stripped hex socket, if one can be driven into it tightly. I certainly did not mean to drill through the plug!