Symptoms of a decentered element.

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?

 

Yes, particularly if the lens element out of alignment is an element that corrects CA.
You might want to spend some time checking out how lenses are made, and why they have so many different pieces of glass in them.

Why not ask Nikon Canada Service about repairs. It's pretty hard for anyone here to speak for them.