There is a bug where you can open the barn without going through the garage and getting the note on how to start the car and valve first, but it doesn't impede gameplay, just confuses the objective. If you have the processing key, RMB on the correct door of the smaller building next to the barn where you picked up the key to use it. Thank you for making a video! It's gonna be a big help when I revise it for the full game.