uuuhhh never heard of fillin the box up that way before there is one at the front on the side yes its a 24mm bolt thats the where you fill it up from the drain plug is at the bottom of the box at the back next to the n/s driveshaft and again thats a 24mm bolt if uve been fillin it up from the very top like you said i think you are gonna have some problems!!!!!!!!!!!!!!!!!