Hey, James… if you’re more or less skillful with your hands, you’ll be able make some minor fixes on your horn. Needless to say it’s a must to know every detail of it. Take your time to watch and learn every key action, how the toneholes open and close, under what fingering conditions, etc. Pay good attention to those keys that operate with some “exceptions” depending on which others are pressed, for example the G#.
Good luck!