Also Haasman, this 'plunger' you mention - is that to help with the refilling of fluid or actually removing the fill-plug?
It is to fill the diff after draining. It is a clear plastic tube with a connector that goes on the end of the diff oil bottle. You can use it to squeeze the new diff oil into the differential. Be sure to check the fit of this "spout" to the differnetial oil bottle.
Hope this clarified.