I've noticed a lot of remasters seem to suffer from loudness and compression, I think that is worth taking a look at in a future video. Original masters of CDs have a better dynamic range for sure, and the clarity of the music winds up suffering when it's compressed.

Mechanically, two issues. 1st is the belts, some loading mechanisms rely on belts that go bad over time, and that is why the door won't open. This very much depends on who designed it, but that same problem can happen in a different situation. Machines that don't have belts have a series of gears, and those gears have a grease on them that gets sticky and hard over time. When the mechanism is taken apart, clean off the grease and apply a fresh coat, it should work properly. Electronically, that one takes a little more skill, testing parts of the circuit and making sure that all of the caps and resistors are in good standing just requires a little more research and a multi meter, but there is a lot of good info around on the web, and while there is a bit of a learning curve it's worth the time in my opinion.