The entire purpose of the design is explicitly to keep the tolerance for leaks at a level where, to quote the whitepaper "standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density"

Section 4.5.4 otherwise covers this, and does point out that for large leaks, braking would be required, but smaller leaks are intended to be dealt with as part of regular maintenance, with no indication that it'd need to affect operations.

> Regardless, the core structural engineering is the focus of the criticism, not whether it might leak.

That may be so, but most of the criticism I've seen of it appears to just ignore large sections of the whitepaper.

EDIT: For example, with respect to handling expansion/contraction, consider that the world has gas and oil pipelines that has to deal with far worse conditions without leaks.

Gas and oil pipelines typically use expansion loops to handle thermal expansion/contraction by flexing the pipe: http://demonstrations.wolfram.com/PipelineExpansionLoop/

Because the hyperloop cars are discrete (as opposed to the continuous flow in a pipeline), I'd expect them to cause a lot of stress on the pipeline walls if they had to run around the bends in an expansion loop.

That's why Elon's plan is to let the endpoints move instead.