I'm getting ready to wrestle my NP203 back into place. where is the fill hole on these? there is a square plug with a 1/2" drive type looking nub on it. that looks like it will be about halfway up the np203 case when it's installed. should i pump gear oil in that sucker? is 1/2 way full sound right? My manual is one of those plain vanilla haynes/chilton types and shows drain and fill plugs that are not present on my tcase.