Agreed, that's a separate sleeve. It doesn't appear to be keyed.
Some PB Blaster lock up the flywheel with a vise grip (or such).
Clamp on a vise grip to the sleeve and try moving it-both around the shaft and outward smacking the vise grip with a hammer. Some heat may help as well (at least a heat gun).
Some
gentle hammering with an air hammer may help bust any rust internally.
.