The long bolt: If you are talking about a bolt that is not a cover bolt, that is the bolt that holds a thrust pad in place. It is a brass pad that stops the ring gear from distorting under heavy load. I don't know exactly what you do from here.
As for the filler hole, you just purchase your gear oil in the plastic bottles with the pointed spouts and pour it in. The level should be 1/2" below the hole when not warm.
