My left fan was in trouble and seemed to stop after a prolonged period of emitting _really_ loud noises.
Bought the fan from ifixit. Fired up the relevant guide (which I already familiarized myself with in the weeks before) and just did it. Was a quick operation (~30min, including paranoid checking of screws/guide/electrical tape/etc.) and went great!
The only thing that's a little hard to do was getting the keyboard to seperate from the fuselage. But like mentioned in the comments: it just needs little unusually strong help and everything's smooth from then on.
Guide, pictures & comments are all accurate. They displayed everthing that was present in my 5 year old device and helped me to do what I wanted without worrying too much. But I worry too much anyway so don't let my worrying distract you ;)