A broken oscilloscope is a whole EE education. It’s a combination of reverse engineering, understanding the signal processing chain and practical skills. . Really you can learn a lot about impedance, high frequency design,, frequency compensation, differential amplifiers, Schmitt triggers, power supplies, High voltage safety and even a bit of physics with a dead one. Not to mention an education on construction and production of an actual device including mechanical considerations.
Problem is you usually need a working one to fix it. Buy a working one then a dead one.
Reverse and forward engineering are both important. The skills you learn above will help you when you jump into an actual job and get a turd on your plate. A lot of people just start again because they can’t reverse engineer and document something.