OK Retro Honey, just for you. I did some work on this. Actually the sleeve didn't need heated up, I just pryed it apart, it kinda snaps on. Being it's not going to be reused, doesn't matter if it breaks or not.
Now for the heating up or cutting the large shaft part. I'd suggest don't do the cutting at all. There's a reason I'll get to. As far as heating it, OMG, took forever and ever using a propane torch. Mapp gas gets hotter, maybe that would be better, but the propane does work. DO NOT BREATHE these fumes. I did this in the garage with it closed up. I am feeling very sick now. Sore throat, eyes burning, sniffles, upset stomach etc. So do it in a ventilated area. I didn't see a good place to hit it with a BFH to help it along that wouldn't possibly hurt a joint, or knuckle, or bend the shaft. So squared up the connecter on the ground and pushed down as I heated, and why the fumes were coming straight up in my face. Finally after about 15 minutes of heating it up, and watching this nasty stuff leak out of the shaft, it let loose and the whole shaft finally collapsed and the bigger shaft ate up the little shaft.