Why would my GPU rust?

[Paparahzi]

Windows 7 Home Premium x64
Asus Z97-K Mobo
Intel(R) Core(TM) i5-4670k CPU @ 3.40GHz 3.40 GHz
Corsair Vengance 8 GB(2x4GB)DDR3 RAM
EVGA GeForce GTX 780 Ti Superclocked ACX 3GB
Corsair CX-750 Modular 80+ Bronze power supply
Noctua NH-C14 CPU Cooler

http://Imgur Pictures of my GPU
It all started when...
"Playing black desert online I experienced a system freeze, then black screen and then game crash. I restarted the game client only for the same thing to happen a few moments later, but this time my whole system didn´t recover. I did a hard reset to find verticle blue lines/ dots / artifacts flickering on my screen, after another restart, the same thing. I then uninstalled the gpu driver and reinstalled the latest nvidia driver and was prompted to restart my system. After restart I had many more artifacts on my screen, but this time red. When I checked the driver it said Windows had disabled the gpu (code 43). From there I tried 2 days of various maybe fixes from forums posted from nvidia forums Microsoft forums and other reputable forums. Such attempted fixes include, using DDU to uninstall the drivers in safe mode and re installing the latest drivers, updating Windows, updating my bios (Asus z97-k), ´re-seating the gpu, cleaning gpu(wasn´t very dusty, although I noticed some greasy/oily residue on the backside, and some minor corrosion on some metal parts). I have also reformatted/ clean install of my Windows 7 OS(done twice, trying multiple driver installation techniques, using methods suggested on nvidias forums)..."
That was the message i sent to PCCG regarding my busted GPU...

They replied with...
"We have received your graphics card back in for warranty, however upon initial inspection we have found some Corrosion on the cooling array behind the fans and the back of the PCB. (please see attached pictures)

Please note that this damage is not covered by warranty, however we will organise for assessment with the distributor to see if we can have this repaired for you.

Although we can generally have these items repaired there is a chance we will be rejected or charged for the repair."

My questions are, why would my GPU start rusting in the first place? And should it be under warranty?(I've only had the GPU for under 2.5 years) I use it under normal conditions, the house/room is not humid( i live in South Western Australia).

Sorry for such a long post, any insight or comments will be much appreciated.

 

[Colif]

Are you near the coast?
http://superuser.com/questions/37245/how-to-prevent-corosion-damage-in-a-salt-air-environment

https://linustechtips.com/main/topic/382134-sea-air-corrosion-rust-need-help/

 

[Paparahzi]

Well I live relatively close, maybe a kilometre, I never have the window open tho, plus I've had other systems running in the same room for years with no rust... I looked at some of the threads you linked, I noticed someone there using the silica gel packets which I also have inside my system... I'm a little P.O'd because my warranty doesn't cover the damage and there's no way to prove to them I've been using my system in a normal environment.