Oh, and another thing. You can clearly hear the difference between the working (bottom) and non-working (top) drives. The non-working drive is missing the door, but I assume that wouldn't affect functionality, right? I also learned that I kinda have to press down on the top of the drive for it to read properly when I tried it out again earlier.

https://www.youtube.com/watch?v=Jw8UrXmz93U

You need to study how this drive is constructed. It just needs some grease somewhere, which is why it isn't "locking down" the disk into a position where it will read. Or it's dirty/corroded/something of that nature. I would watch all moving parts when the disk is inserted, when you push it in to the secure position.

Then get some grease, a tiny screwdriver (you may or may not want or need to do any disassembly) and apply to those contact areas or joints, work it in there until it behaves as designed.

Alternatively, something like a spring is out of place or broken. It's very helpful that you have a working drive, so you can see exactly what should be there.

Sorry for the late response, but thanks for your tips. I bought some grease and will probably retry this fairly soon.