Glue will not hold. If you have a dremel drill press you can take the truck off the car body. Place it in the drill press vice with a wood strip against the end of the knuckle of the coupler. Make sure the knuckle is closed. Next take a very small drill and drill down thru the coupler body and the closing portion of the knuckle. Place a cotter key in it. The coupler will not open again.
bruce