Hi Pedro,
as far as Germany is concerned, I can come to think of two addresses:
1. Horst ENZMANN, Kamerareparaturen, Meissendorfer Weg 8, 29308 Winsen-Bannetze,
Phone (0049)-5146-8314
He has so far fixed a Contax, a Zeiss Ikon and an Ica for me, all now perfectly working; he is a specialist for Zeiss Ikon and Voigtlaender, but I have also seen screwmount Leicas in his workshop myself, and he told me that due to their comparatively simple design, shutter curtain replacement and speed adjustment are no problem. Cost for repair is between €€ and €€€ depending upon the number of hours it has taken him to fix the problem. As he loves cameras, he doesn't make you bleed too much, in my case it might have been €€€€ otherwise... Cameras have been sent to him from South America because of his skills!
2. BATCHVAROV & THIEL Kamerareparaturen, Sybelstrasse 19, 10629 Berlin, Phone (0049)-30-3238319, Fax (0049)-30-3238696. They are reputed to fix any problem with vintage cameras, but I have no experience so far and therefore no idea about the prices.
Good luck!