Rattling Citizen manual

My newly-acquired Citizen Homer manual rattles noticeably, and without the caseback the movement wants to fall right out of the case, only being held back by the pin. Is there some retainer clamp or screw missing here? I have no idea what I'm looking at. I want to get it serviced but the guy I usually take watches to is across town and it's likely it'll be some months before it's safe to risk the trip. I'd be grateful for any insight.