Thin horizontal grey lines - T-Con Board, Display, or Software?

Hello everyone!

I recently purchased an A1398 for myself as a working project. That is, it mostly functions and I intend to use it as my main computer, but it has an issue that I’m stumped on. Namely, it has uniform thin grey horizontal lines across the screen. I purchased it from someone who says it was fine until he reset the MacBook to retire it as a secondary computer after purchasing a new model. Lo and behold, once he updated it, here were the lines. I’ve re-pasted the GPU, tried a different (same year) LVDS cable, and updated the firmware to Mojave and nothing has affected it. The lines do not appear on an external display.

The other screen aberration I have experienced is a very strong stalling/ghosting with some rainbow and shadow effect. Essentially, the screen freeze framed and 5 seconds later it would return to active control. The mouse moved and you could make changes in that frozen time, but you wouldn’t see it until the screen resumed functioning. It went back and forth like this for some time, and restarting the computer helped manage it. It was mostly common before I upgraded it to Mojave, and it hasn’t shown up again since. I also stress tested it and the issue did not re-occur, despite high heat. I’m hoping that is resolved by the updates to newer firmware, but wanted to include it for the sake of thoroughness.

I’m hoping someone has encountered this so I can move in the right direction. I’ve decided to make this my main computer, so I would like to fix the screen if possible. It would be a real bummer to buy a replacement display without fully exhausting all avenues of fixing my current one.

Thanks everyone!

Cheers,

Aaron

P.S. It is difficult to capture the lines in pictures. Zoom in on the picture and you will see them. It is much more apparent when looking at the screen in person.