vintage Anniversary Clock KUNDO 50's GERMANY Kieninger Obergfell dome RARE OVAL.

Bought this from a local estate sale . I had a spare key which I used to wind it up . After winding the clock it seems to work but after a few minutes of pendulum moving t slows down and gradually comes to a stop . I believe it will need to be serviced . The glass dome is in very good condition no crack . The metal on the clock shows some tarnish and some scratches please see all pictures does not come with the windup key