How do I take apart my Oster Professional blender?

The coupling in my Oster Professional fractured/shredded along its horizontal axis. I can't remove the remaining part of the coupling, working from the top, because it's threaded onto a part that spins.

I can't take the machine apart to get at it. I haven't been able to remove the metal collar the jar sits in. I can't even tell whether that part is supposed to come off. The rest of the machine has no screw heads showing.

Is there some trick to this? I don't want to lose a $60 blender for want of a four-buck replaceable part.