When N=10, and each one is a strategic asset, which, if found disabled, would cause every major head of state in the world to reassess their long-term global postures on technology, defense, and relations with the US, it doesn't take much to buy that plane ticket.
I worked as a mechanical engineer in the nuclear power industry for a couple years and this happened frequently even for normal power plants.
Like, one of the first projects I worked on was diagnosing a malfunctioning valve where most of the work was finite element analysis on computers, but we still had to send someone to take measurements and temperature readings since the company that made the valve no longer existed (and I'm not sure how you'd ship something like that since it was very large and used with contaminated water)
I agree that the cost of the plane ticket is minor but this IMO makes the proper procedure starting with lab replication even more important.
You usually get much better results when you work in a well equipped lab and have access to the right experts. For anything non-trivial "replicate, understand, fix, deploy" is a much better approach. Not always possible, and when it is not going to site may be the only option, but it should be fallback, not primary path. My 2c.
