Hello, if you haven't solve that, the problem isnt at the bottom mechanism.
It is at the tonearm liftplate that when the tonearm is at the end of the disk the liftplate find the tonearm C, and can; t move any more.
You have to use a sandpaper for the tonearm liftplate so it will have a few mm space from the C of the tonearm. see the photo :