Hi all
I've changed the card of my 2012 rMbP as well.
I got it as mentionned earlier from Taobao, through some people I work with in China.
I switched the card, had a very hard time plugging the antennas back, but ended up having the card working.
A few days later, I realize some coating on my screen was starting to peel off. check the forum, you'll see other threads on the subject.
Since I already got my screen replaced twice because of hot pixels, I decide to go back to the Apple store to have it replaced once again (congrats to the Apple client service, they accepted to do it at no charge even though the mac was over 2 years old, without Applecare).
I didnt want to be a hipocrit, so I just left the new card on the system. Thinking they might actually plug the antenna back in better than I did.
Anyway, a tech guy calls me, telles me the card isn't been recognized by his tools, I explain why, and tell him I'll bring the original card back in.
A few minutes later, he calls back, telling me everything was working OK, that they changed the screen and that I could pick up the machine.
He warned me though : the card I had bought was missing the thermal insulator pad that should be there, and that I saw was indeed on the original card.
So I reopened the machine, unplugged the card without removing the antennas and put that pad from the old card to the new one.
The tech told me this SHOULD be there, cause if the card was to heat up, it could damage the motherboard...
So be warned, it's a detail, but one must know this before proceeding...