I've read elsewhere a while ago that the "logic board" failure is systematic of this issue as well, but hard to get anyone to acknowledge it.
I am actually Australian, currently living in the US, so i wonder if i had the part replaced in the US, whether i could walk into an apple store in australia and claim a repair warranty of 2 years?! No idea.
You are right. AMD GPU is prone to internal bumps problem after a certain period of time. Unfortunately ,you cant prove it because you would need to watch and take notes of GPU internal changes under microscope.