........and what they are plated/tinned with will play its part in deciding how long it will take for the problem to show itself.
Damp does get everywhere, including the insides of cables through what is often thought of as an impenetrable barrier in the area of the crimped terminal. Unless there is something extra there, it is an entry point. Once in, it does its evil over time. Bigger and/or plated wire just takes longer. When it does become a problem, trying to reterminate is generally futile - stripping the sheath back and cleaning the black muck off only shows you that the wire is now 99% black muck with almost no wire up the middle. Repeating te process only reveals that the entire length of the wire is affected.
I suspect that the black stuff is the same as that which appeared (intentionally) on the plates of copper ovide rectifiers before the new-fangled selenium appeared. Except that the rectifier makers intended it that way, inside the cable it is another of Mother Natures home made components, and Mother Nature is a bit random in her quality control.
Following the good reports that I have seen of it, I am hoping that the CorrosionX will do a better job of protecting than the WD40, but it will only be used on new plug-ins and rescued radios. I not only sail in salty water, but live on the bit of UK coast possibly most exposed to salt laden prevailing wind that has a big town perched on it, so if it works for me, it should be universally good. Time will tell.