I was trying to deduce if you took your laptop apart. If your saying the copper was shiny , I take it you did ? I would say you messed something up. You have to be very careful with laptops, the torque,tightening sequence on the lid.
well for one, its an nvidia but you likely clogged or didnt clean the fan right, or actually messed it the actually card up, touching it, jamming it, u probably budged it making heat conductivity bad. if not that, it might be the software and drivers
i won't recommend opening a laptop without much knowledge...
and since its only few months old you should have made use of warranty provided by the company.. and now you void your warranty by opening it.. its a big mistake done by you..
now take it to some tech pro and get the entire thing checked, your manufacturer is not going to do anything on it now..
He obviously hasn't messed with anything to cause the GPU to overheat, think about it....
It was working fine, then (suddenly) the GPU idles at 80C, THEN he decides to take the cover off the laptop, so the problem was already there before he did anything.
@OP uninstall the old drivers and install the latest driver from nVidia's website.
You got the order wrong. He took the cover off to clean it two weeks ago. Then today or two weeks after its now hitting 80c.
Something may have flexed, shifted or even torquing of the plate has effected components, as show here. Its one possible explanation.