PS2 Slim (SCPH-77001) Disc Not Spinning (Images and Video Provided)

After adjusting both potentiometers and cleaning the lens, discs still wont spin. I have noticed that discs will sometimes jerk a few degrees, like its making an attempt to spin. The door sensor in the back of the console is missing, and so is one of the screws holding down the disc drive (I have also tried applying pressure to the top of the console with the disc inside, to no avail).

What should be tested before replacing the disc drive entirely, and will the missing door sensor cause future issues?