I had the same on 15" rMBP, basically touchpad's edges "printed" on the screen with some more "stains" in other parts of the screen. It began with a barely noti

I had the same on 15" rMBP, basically touchpad's edges "printed" on the screen with some more "stains" in other parts of the screen. It began with a barely noticeable horizontal line after around 8 months and got progressively worse and worse up to the point it was taking around 1/16th of the screen. I always used water to clean the screen. Ended up paying ~300 EUR for a replacement screen, no issues since. Apple didn't offer replacement for free.