Here's the story so far. I bought a new PL 8-18 from a 3rd party seller on Amazon. I was generally happy with the performance, but a few of my test shots kept nagging at me. Something was not quite right. With careful testing I was able to narrow the issue down to a bit of a surprise: at 9mm the focal plane tilts sideways, closer on the right and further on the left. It's basically fine at 8mm and 10mm, but at 9mm it's shot-ruining in close focus, and enough to marginally degrade the edges at infinity. Okay, case closed! File a return request and buy a new one. The new one arrived a day or two later, before I had packed up the original. I did a close focus test and yay, the focal plane was level at 9mm. Then I did some distance tests and hrmm. I'd just spent hours testing the first copy, so I was getting very familiar with the scene, and it didn't look quite as good. I could swear those edges were worse. After more careful testing of the two head to head, I determined the second was slightly worse across the frame at every focal length. At 9mm, where the first was weakest, it was a tossup between them. But at 8mm, 10mm, and 14mm (I mostly want this for ultrawide, <12mm, shots), especially wide open, the replacement is distinctly worse. Now I know why some people are saying the corners are soft. As it stands, I'd rather take the devil I know, and keep the original, and just be very careful in how I use it at 9mm. Or I can try much luck and get a third copy. On one hand, I'm aware that no zoom is going to be perfect, and I feel like I'm chasing a dragon here. With two samples flawed (at least relatively) in ways I can detect, I'm not very confident getting a third will change anything. And I'm definitely getting sick of taking careful test shots out my window. On the other hand, do I really knowingly keep a brand new, $1100 lens with a clear defect, even if the defect is only in a narrow part of the zoom range? It was bad enough I was willing to return it the first time, before the replacement showed up. Could I resell it later in good conscience? And life is too short for bad glass.