I would actually expect leaks to be easy to detect. Just run a high-frequency high-voltage plasma discharge detector on a skeleton vehicle. Wherever the discharge quenches you have a leak. Barcodes laser etched during construction could help you localize the leak to within a few centimeters.
Pinholes might be repairable by pressing a sapphire drift against the leak and melting the metal underneath by shining a laser through.
True, but this either has to be done by paid union labor 50 feet off the ground near 1 tor vacuum or by a heck of a robot. The union guys will be certified up the wazoo and paid to match that and persnickety about it. The robot will be and engineering marvel and a hell of a good idea.
I mention in another reply that Mr. Musk also has plans that involve vacuum differences and not a lot of wiggle room. On a trip to Mars a robot hull fixing machine would sure be nice to have.
Pinholes might be repairable by pressing a sapphire drift against the leak and melting the metal underneath by shining a laser through.