Not to detract from Deonasis's observations, but I just checked out my Black Metal Unicron and indeed it might be bad news...
That section is designed with a spring and pin assembly for the hinge but the actual plates do indeed come off.
It all really depends on what area is detached (The hinge or the plate), meaning you'd have to open it and have a good look to properly diagnose IMO
@Verno: Do you have a physical copy of DoFP (BOTCON '06 Comic) man?