[Rvallette]

I had that problem and it was easy for me to fix.

First you have to take a Hair drier and carefuly warm the arm. You can do this with hot water too.

Then pop out the forearm from the elbow. You need to do this carefuly, dont rush this part.

The elbow is like a revoltech joint. In the middle of the two pieces that form the elbow there's a gap. Inside this gap-canal or corridor ( sorry 'bout my english) theres a tiny piece of plastic that connects the piece that broke off, and the other side is like a ring shaped plastic that connects to the center of the revoltech joint.

You have to separate the revoltech joint in order to glue the piece in an appropiate way.

This part when you separate the two pieces of the revoltech-joint was the most difficult part to do, and easily take me more than 20 minutes to do without damaging the joint. I used to do this a hobby knife ( Im a gunpla-macross-kit modeler)

You glue this part that broke with super glue, cianoacrylate.

Then you put carefully all togeter.

Hope this helps

Its not difficult, you just need to be patient, or you can ask a friend with hobby-building skills that assist you in this surgery.

Saludos