The ID argument is, and always has been, that because 1)such-and-such a biological system requires all of parts A,B,C,...,Z and 2)possession of only a subset of those parts conveys no advantage and thus is not preferred by natural selection, then the biological system in question must have arisen fully-formed like Athena from the forehead of Zeus.
The fact that components of an allegedly "irreducably complex" system serve other functions in their own right refutes premise (2) -- if A does something useful, whether or not it is related to the function of the A,B,C,...,Z combination, then natural selection will tend to keep it around even without any of the other components. The entire argument thus crashes down.
Behe's argument is simply a bit of prolix razzle-dazzle designed to focus attention on premise (1) in order to distract attention from the failure of premise (2). Unfortunately, his irreducably complex argument cannot function without both of them.
And for a component to "remain" around it must be maintained, so will it will be either unchanged due to its criticality for its present function(maximum fitness and "unavailable" for cooption) or be driven towards criticality for that function(seeking maximum fitness and "unavailable" for cooption) as predicted by Darwinian evolution. And as Behe makes clear, you build a straw man and knock it down by your mischaracterization of his argument. Premise two is a false representation of his argument. He again has clearly stated above The system can have its own function, different from any of the parts. Any individual function of a part does not explain the separate function of the system. "