Medis auxiliary rangefinder

Just taken delivery of a lovely little Medis auxiliary rangerfinder. As always the eBay advert was "used" which means it should work but as far as I can tell the second image is way too far to the right. It's almost separate from the main image, such that when I turn the distance dial there's no way two points can ever match.

Am I missing something with this little accessory? Or is it knackered? And if so, can it be fixed? I've attached an attempt at a photo of what's going on.

A rangefinder consists of a movable mirror or prism and a fixed transparent mirror. A cam mechanism controls the movement of the movable mirror. The mirrors were likely bonded in place and one has come loose or the cam mating is off.
Post pictures of the outside of the rangefinder if you cannot figure out how to open it and the internal mechanism if you get it open and can't figure out how to adjust it. Rangefinders are set up on infinity.

On mine you have to adjust the images to a given distance by turning the knob in the middle of distance wheel. You may also have to loosen the conical set screw also in the middle of the distance wheel. If that doesn't work you will have to go inside or return.

I think there's more to this than calibrating/adjusting. The second image, the one that is moved by turning the distance knob, is totally separate to the main image. As in the attached photo which is taken through the viewfinder of the rangefinder. There are two separate images which never overlap.