Before you start having to take things apart to see if you have it, let's try this first.
It's kind of an un-natural shift to get the shifter in low until you've done it a few times.
Sit in seat, tractor in neutral, grasp the shifter with your hand, roll your wrist to the right until the lever won't go to the side any more and then push forward. It is quite a bit over and down in it's travel. If there is much wear at all you will think you are going to leave skin on the edge of the battery box.
this is how far off the pattern the shifter is in low one one of mine, if the battery box was on it would be all most rubbing it. Try it several times before you give up, it does take practice! try this and post back - it you have no luck we'll guide you on looking deeper!