+1 ATF fluid and acetone is my go to for frozen parts. I normally soak it for a day or two. Then, I tap the parts with a small ball peen hammer. Then, I hit it with heat. Then, I take a can of compressed air, turn it upside down, and freeze it with the freon from the can. (expansion and contraction.) Then, I try to turn it. If it doesn't turn, it goes back in the bath, and I try it again the next day.