The front axle on my M6040 is vented. Dead center, top of the axle housing. A VERY difficult place to locate. It's a screw in plug with a nipple. Rubber hose attached to the nipple. Hose goes up - connects to a steel pipe - terminates in a 180 bend at the very top of the radiator.
Makes no mention of this in my Owners Manual. Had to put a small filter on the end of the steel pipe. Mud daubers like to fill the end with they eggs/goo.