Problem with 24-70 F2.8L USM

[Mikeinminn]

Hi all. New to the forum. I just bought a used 24-70 F2.8L USM and noticed that even the center sharpness at 24-35mm F2.8 was poor.

Obviously, the weakest spot in a lens is at the wide end but the difference between pictures is stark and surprising in light of the ISO chart for this lens.

Photos of the wheel were taken in shaded outdoor morning light manually focused on Live View at F2.8 24mm 1/250 (zoomed all the way in on the camera's review screen) and about 40mm F2.8 1/250 and backed away so that the object takes up roughly the same amount of sensor space. The problem only shows up at when the lens is opened up and at infinity. It looks and feels like it hits the focus limiter before it comes to focus from 24-35mm or so.

This may be happening at infinity at longer focal lengths too as the pictures of the tree show. The tree photos are all taken at 50mm infinity with different F ratios starting with F2.8 then F4 then F8. All pics are approx. 100% crops which are then re-sized and compressed for use here. When I stop the lens down, performance between focal lengths is similar.

Is this sort of performance normal for this lens? Is the wider aperture somehow showing up a focus problem that narrower apertures mask? I'm just trying to decide if this should be returned or just sent to Canon. If Canon charges too much, I may as well just pony up for any new ones that are still available considering the price that is common for a used one. Thanks for any input.