It looks like a retaining ring but it's continuous, and there is a small notch where something could be inserted, but it doesn't seem to want to come off. I remove the pulley set screw and it can move and is obviously not connected to this mystery end piece.
Because it has "teeth" and the notch I don't think it's a bearing. Hard to get a good idea what it is because picture is blurry. Would help if you also had another picture that wasn't close so one could get the "big picture."
You might want to try the DIY discussion group, they probably would be interested and more knowledgeable.
It looks like a cheap keyway bushing. Probably a press fit thats corroded. Try penetrating oil. If that doesn't work try heating the pulley (not the shft) with a torch. You might try a bearing puller, but the shaft may be too thin.
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