Abstractions are not always leaky. Often the “leaks” come from wanting to push past the bounds of the abstraction (for performance, additional capabilities, whatever). A good abstraction, if used as intended, needn’t always leak.

People also often define “leaky” as “can break”, which is kind of unreasonable. The notion of a data stream across a network is an abstraction over many layers of complexity. People often say it’s leaky because of packet loss and failed connections, but that’s not a leaky abstraction unless you define the abstraction to not include a failure mode.