How can I fix my Kundo Anniversary clock?

I have a Kundo (Germany) battery-operated Anniversary domed clock. It has operated perfectly for over 30 years. Now the clock itself has stopped working, (it has stopped ticking and the hands no longer move), though the pendulum still appears to be fully functional. I cannot even decide how to take the back off to check for possible lubrication needs as I am scared of breaking the plastic case. (Possibly it is a press-fit?) I have replaced the battery....:) I can find no serial numbers, model numbers, etc. All I can find, on a paper sticker on the bottom is "641 50190 1 2" which could esily be a merchants stock number. Any advice please? Thank you in advance.