Our tractor has two cover plates and the two are seperated by a cast wall.  There was a drain plug in the side of the casting that we filled up to.  We found in a  factory manual that we should run 140W in the summer.  It all completely runs out of the upper trans. and sounds like the gears have no oil at all.  Our donor tractor was a  newer row crop and it was like you decribed.  Our tractor originally cam on steel and has no 5 or 6 gear.  But ours is completely seperated.Thanks