I just took my D300 outside in the sun with the protective cover off, and it shows the streaks you mention. The streaks are vertical and not uniform. It really does look like someone did a sloppy job of wiping it with a dirty cloth! As I have not noticed it before, I am not sure if I need to do anything about it. I bought my D300 about a month after they were introduced, so the problem has been around for a long time, and not just for recently manufactured cameras. I also checked my D90, which should have the same LCD, and it does not show any streaks.