As soon as the assembly was out of the case, it was apparent what the problem was. That chunk of aluminum (arrow) is half of a shift fork. The other half was still attached to the shift rail. We figured it was the Reverse fork, and we were half right. Turns out it is the Fifth gear and Reverse shift fork. If we were doing this on our own, this would have put a big damper on things. Fortunately, Dibs knew exactly what other parts needed to be checked, and where to get replacements. More on the fix next time.