So I have an old 80-200mm AF (push-pull) and I really haven't touched it much since I got it for 60 dollars and it has... certain issues. Sometimes it is sharp, sometimes it is not. It creates circular bokeh sometimes, depending on what focal length I'm shooting at. I think it has a decentered element but I'm not exactly sure. Can a decentered element cause CA at wide apertures? Will stopping it down "correct" some of the decentered effects? Will Nikon still repair this old lens?