[gtxracer]

It's okay, that play will go away when you assemble the rest of the truck. I'm not sure why it moves, but I assume Traxxas made it that way so you can remove the diff without taking out the bulkhead. When I ripped off half of my rear bulkhead I had the same thing happen to me. I just kept going and it was solid by the time I was done. I've ran it since then and it's fine.