Well...if you are still cooking it in anti-freeze...I would use a piece of hard wood dowel or the handle of an old tooth brush, and go in through the backplate to try and push the sleeve up. (while it's still warm ) The anti-freeze will also act as a light lubricant.

You might need more heat though...

I've run into some stubborn instances where I had to use either a heat gun or propane torch to get the case hot enough. Try not to get it too hot...when you see wisps of smoke from residual oil, that's about as hot as you want to get it.

Hopefully, that rust won't grind in (in between the sleeve and case ) and cause the sleeve to bind-up in the case. If there's any way to clean at least some of it off, I would do that first. (with Q tips, and/or maybe whittle down a popcicle stick to try and burnish some of it off )

Carbon around the exhaust port (if any ) should be cleaned off too.