Thanks everyone. It was really frustrating when it broke, I was in the middle of photoshoot when it happened. I stopped and I just sat there pissed off staring at the break, then began disassembling it to get a better look at the break.
I have had a chance to calm down, assess the situation and work out a solution thanks to mechaninac and aaajin for the tips on the glue! I have plastic weld and will go with what you have suggested. I don't have the modelling skill to try and clean up the break, so I will keep this one permanently in fighter mode and put Super Parts on it to cover the break.
@Loop & @Valk-1S, that is pretty much what happened. When I was bending it down I noticed that hinge was bit tighter than the other, but got it to Battroid mode. When I was transforming it back it was even tighter almost frozen and that when it broke.
@F360, I would check those hinges before hand and slowly work them to a few times to loosen the hinge before doing a full transformation.
@Shukenzero, thankfully this was not my only copy.
I hope no one else encounters this. Here I was avoiding the VF-171 CF because of the breakage issues, and now I have a broken VF-25S...