Help with constellation reference

Good afternoon, I picked up a couple constellations this morning. Both need service and have mottled dials from moisture, but one needs a caseback and I'm not familiar with the reference. I know you all can help.

Serial is 15M range on a 505 movement which puts it around 1956 but it's in a straight lug case. It may be an incorrect upper case as we also found a loose 2852 caseback.

What do you think? I'd like to get it correct. Thanks!

Yes, incorrect mid case - should be a 2852 (most likely).

Thanks! I'll start looking for a mid-case. If anyone has one, let me know. 😀