Have not tried the acetone/trans.fluid mixture for stuck parts but have used plain trans. fluid with a good deal of success.
Too, you can try this as well in the garage or outside.
Follow Pahoo's instruction of unloading, removing bbl. , propping upright and plugging nipple. Boil water and fill bbl with boiling water to let bbl get hot. When bbl gets as hot as you can get it with the boiling water, use heavy gloves to grab bbl and quickly dump out water and re-inst. bbl in vise. While steel is still hot, KEEPING YOUR HEAVY GLOVES ON AND FACE AWAY FROM MUZZLE JUST IN CASE OF FLASH pour your trans. fluid down the bbl. Let soak for a couple days.
Since the flash point of ATF is anywhere from 420-480deg and water boils at 212deg. you shouldn't have a risk of the ATF flashing but proceed with caution just in case.