Line bleed is not necessarily a defect. An ISF calibration can help with line bleed slightly, but not that it will remove it completely. It is just the way plasmas handle the picture. Some tvs are better than others with it.
If you are unhappy with the panel, you need to prove that it does have a defect. Look at it from the side and see if you have circular blotches all over the screen. Run a 3d movie and see if your 3d glasses and tv go haywire in a bright white scene. Those are defects. That is why my panel is being replaced, as ordered by the tech.
Keep in mind, LG has no obligation to give you a brand new model tv, but only to replace the panel if defective. If they do not have any panels available and they cannot be ordered, then it might be possible.