I think I have to replace the power buttong

You'll likely have to replace the keyboard. Which I'm not sure how doable it is on those models, but it does require removing the motherboard. Then you'll have that black tape going around the edge of where the keyboard rests. I'm not sure why there's not a guide for that, unless they're riveted in, so maybe check out the guides for the models a year or so later and you should be golden. They route the PB through the keyboard flex so it requires that whole part to be replaced. Should be cheap enough to replace, just need the tools and patience. And also Magnetic mats. A lot.