13ZN find

Sorry, not going to share my cost estimate here, as revision costs are dependent on the condition of a specific watch, complexity of the movement, necessary spare parts and other variables as you certainly know. Therefore you have to send your watch to Longines HQ in Switzerland for their assessment.

What I can say and already have said is, that the costs are much lower than what other Swiss watch brands (Rolex, Patek,…) ask for servicing their vintage models. Be prepared however to spend a minimum of 1,3k - 1,5k for 13ZN or 30CH calibers, depending on a.m. variables (plus 250 Euros for Extract of the Archives or 350 Euros for Certificate of Authenticity, if desired).

Then be happy

I think you can find a good watchmaker that will fix this watch for a fair amount of money. No need to send it to Switzerland.