3ds top screen darkens if pressed

I recently bought a used OG 3ds and the top screen looks fine most of the time, but with hand pressure the screen darkens and sometimes also looks red-ish. This sometimes also happens at certain angles (not always though). I am aware that this problem could be caused by ribbon cables. They don't look damages so I tried to re-seat them and the problem still occurs, even though it is not as bas as it was. Did anyone had the same issue?