Here is one more video where you can easily see most of the bottom mechanism of the garrard. I think that the problem might be on the upper right where there is this lever that seems to want to get nudged by the slider, but it doesn't push it far enough to stop the record.
Can you see if the positions of my parts are the same? There I replaced the spring on the part I'm talking about, so you can see an extra spring dangling there to help you find the part of the mechanism that I'm talking about.
LINK: Some more dropping videos.
Enjoy looking. I need to stop and watching slow motion because there are so many moving parts. If I had a working model to compare this too, then I could see what is different.