I presume you mean that he split a piece off of one of the arms?
Personally I'd get out my old can of Weldwood Plastic Resin Glue. The stuff's hard to find nowadays and you have to buy a pound of it for ten bucks or so (that pound will likely last you the rest of your life) but it's good stuff. As for durability, it's FAA approved for structural use on production aircraft. Epoxy has all the glamor these days but the old workhorse is cheap and good. Do read the label though and use it exactly as directed.
Another alternative, find the nearest Woodcraft and see what they've got--they should have T88 epoxy in a 1.6 ounce syringe for 20 bucks or so--that should do the job nicely.
Or Titebond III--it's not going to be immersed and there should be enough irregularity in the split to serve as a key and prevent creep.