Bad lens? Does this need to go for repairs?

[sjmurray]

I have a 18-70mm Nikon "kit lens" on my D70 that shows a similar problem confined mostly to the lower right corner. It is inconsistent, as I have gone through almost a year's worth of images and sometimes the softening doesn't occur. Also, at 18mm its always tack sharp across the field. So, because of the excellent performance at 18mm I hesitate to send the lens back (still under warrenty). I wouldn't want to get a different lens that didn't perform as well as this one at 18mm. I have a really sharp 28-300, a very sharp AF 50mm lens, a 55 Micro Nikkor, and a classic 105, so I really want to have a sharp wide angle in my bag. When I have photographed a flat textured wall on a tripod a couple of times the problem did not show up, even wide open, but it is quite evident in landscapes. I'm wondering if these zooms don't have internal lenses that can "float" around a bit and get slightly off axis during focusing. Yours looks pretty bad though and I wouldn't hesitate to send it in for repair or replacement.