OK, now I think I've got it right:

Hi! Can anyone help? I think the forward/upper bearing/roller on the _top
back corner_ of my sliding door is caput: how do I get at it? Is this a
standard abec-1 bearing? This is apparently the cause of the latching
difficulty. I can see the inner race on the "post" and the outer race has
dropped down below the track.  TIA, JinNJ