17-40 bottom right corner
"The issue is there with all apertures, very obvious at f8, still noticeable at f11 (see below crops) and doesn't really start to go away until f16. My eye can't help but be drawn to it. If it were a top corner where sky would most often be it would be far less of an issue."
At the 17mm setting, resolution in the corners falls off into nothingness... the lens was released to address the lack of crop camera standard zoom options in the early digital days (D30, D60, D10), but was "backwards" compatible with FF film cameras. If you have a decentered element, it will only make the matter worse, but yeah, for landscapes with high MP sensors in 2013 the 17-40L is best avoided if possible.