gp116126,
My A600 did something similar, and I also thought that it was the eject mechanism. It turned out to be the... beats me what they call it... but it tensions the disk against the guide on the frame when you slide it in. Found a picture of it
here. It's that clear plastic lever arm in the upper right corner, behind the eject button on the top plate. Mine broke, leaving behind a piece that jammed the disk.
After removing it, and the extra pieces, I noticed that the disk is "sloppier" when inserting, but it reads/writes just fine. It seems that the plastic gets a bit brittle over the years, and snaps instead of springs.
banzai