Want to replace the jack input

Unfortunately, the headphone jack on this machine is directly soldered to the logic board. If you can source a part and you're really good at soldering, the part can technically be replaced. Otherwise, it may be possible to bend out the contacts from the outside of the jack. If you check out the picture on this step (step 32), the headphone jack is closest to the front of the picture. I cannot verify that this can be done (because I've never done it), but it may be possible to pry the steel casing off the outside of the headphone jack casing and that may allow you to use a metal awl to push the contacts down into the inner barrel of the headphone jack, making the connection more secure.