This might seem like a crazy idea. Research other garages of that era and see if any had some sort of a small a cupola installed. And maybe some louvers in the lower portion of the door. That may help preserve the character.
If you're not worried about looks, just add some roof vents. That should fix the ventilation problem, but you will still need to address the moisture issues like the others have already suggested.
BTW: That's a cool looking garage.
John
