Whatever the slide is coated with is tough as hell. The "tenifer" finish people refer to (at least so I'm told- someone correct me if I'm wrong) is a metal treatment process and not the black finish that you see. Whatever they do, I've given a G26 hell and it's still fine.
My sweat is corrosive as hell also- I left rusty finger prints on a stainless GP100. I've never had even the smallest amount of rust on the G26... even after cutting grass with it on in teh summer. And I push mow. And I'm fat, so I sweat like hell.