Well, I put that plastic thing back in, still no Wifi (would have really surprised me ^__^).
I messed around with my MBP some years ago and everything was fine. When I opened it yesterday that plastic retainer was glued *above* the camera cable and wasn't very sticky anymore.
On a whim I decided to not put it back in. Now there's now Wifi anymore (did all the hardware reset things, nothing). Can that small plastic thing have to do anything with the wifi?
Thanks for you help!