Why does my screen have small lines flashing across the top screen?

When I turn on my 3DS XL, I see some very small and fine vertical lines going across the whole top screen. It's somewhat noticeable, but when you focus more its not as much. But it's still bothersome to see when I play games since the lines either appear really thin black and white lines or they seem to distort the image in that really find line. Something similar had happened before, but instead of lines everything was somewhat washed out with a white color and I could see some sort of tiny white dots across the whole top screen, but it went away and the screen color returned to normal. When I opened up my 3DS XL, I saw a bit of blueish/greenish gunk on the only ribbon cable located on the back. I'm not sure if its to keep the cable in place or something else. Previously my dog's had also peed on my 3DS, but I put it in rice and let it soak up the pee, could this have done something? Although it still acted and looked like normal after being peed on.