It started having a green/red looking vertical line on it. You can really tell when the background is red as the line turns black. It's a little thinner at the top and wider at the bottom section.
Unfortunately this is bad news.
As far as I can tell that problem is due to failure of a screen panel section. In Panasonic TVs that means that the whole screen has to be replaced.
I have done some searching, and find that screens for Panny plasma TVs do not seem to be available.
However, call Panasonic as their warranty/service centers may have a spare screen for your TV.
When I bought my Plasma a couple of years ago, BB and Panasonic were up front with me and said if the screen failed parts would not be available.
I did buy extended warranty and was told that in event of failure, the TV would be replaced with one of equivalent quality. However at this time I don't think there is one.