I have had no experience in repairing 403 clocks , wouldn't even try ! but I have replaced the original works with a quartz movement using the original dials and face so that the finished result looked like the original. The quartz movement was about $16. plus something extra for hands. It uses a single dry cell battery that lasts about one year , no risk of fire with a dodgy original permanently connected to a 12 volt battery. A good description of the method is in a post on the ponton ( Mercedes) website in which a quartz movement went into a Benz dash clock.
I have had no experience in repairing 403 clocks , wouldn't even try ! but I have replaced the original works with a quartz movement using the original dials and face so that the finished result looked like the original. The quartz movement was about $16. plus something extra for hands. It uses a single dry cell battery that lasts about one year , no risk of fire with a dodgy original permanently connected to a 12 volt battery. A good description of the method is in a post on the ponton ( Mercedes) website in which a quartz movement went into a Benz dash clock.