You think that is what it is?
Water damage or rather the rusting/oxidation is basically the equivalent of contracting cancer for electronics. If it didn't kill that n3DS outright from an electric short, the trapped moisture would have worked its way through destroying those pins and traces over its long exposure period. That's why back then I made a big stink to you about disassembling, bathing the mobo in 91% isopropyl alcohol, and hair dryer + rice/couscous desiccator to pull all the water out, to try to stop it from spreading before it was too late. Exposure to water ≃ omae wa mou shindeiru.
Do you know about the cellphone company of old, Nokia, and their legendary reputation for hardware reliability? As an fart old, I will tell you my little story of once owning one of their later 6000 series models like
this one. I had that thing for 2 years where it was constantly dropped face level high, tossed against walls from family call arguments (I was a fuckboi at the time before the term existed), and pocket impacts from skateboarding. The one thing that finally did the phone in was a little rain water that got in-between its rubber number buttons. Two weeks later, my Nokia died turning on with black screen. My replacement phone, also a Nokia, met a somewhat similar fate but that time it was a laundry washer, lol.
There's not much you can do at this point. Maybe disassemble the n3DS anyway and clean all corrosion off the motherboard with toothbrush + 91% isoproypl rubbing alcohol. It might be the PICA200 GPU that's affected where its neighboring pins are touching each other from the corrosion, causing cross signal noise. If it's salvageable, I suggest spray coating the motherboard with pure silicon lube for extra moisture protection.
