[mylesdw]

I'm guessing at a selector problem. If you can get at the top of the box unbolt the cover where the gear lever attaches and lift it off. On some boxes the bottom of the gear lever can disengage from the selector rods in which case the repair is simple (shift the selectors back into neutral and replace the lever). The bottom of the gear lever may have broken off or damaged, that's another possibility. If you can't get at the top of the box I guess it's transmission out time. It's hard to believe that such a new box has anything really seriously wrong; on the other hand a 472 is a pretty serious motor; how hard were you driving it when it broke?