> Sooner or later one of those repair shops is going to leak those schematics. Either intentionally or accidentally, it won't matter.

While you may be right, the trade secret value of the schematics decreases by the day. If they can delay schematic leaks for months or even a year, that's still a big win. They'll be on to the next generation by then.

While it may seem futile in the end, delaying the inevitable leak and demonstrating to your partners that you made a best effort attempt to keep them confidential is actually a huge win.