A customer in my shop taught me a simple trick for stubborn seatposts
This older guy named Frank came into my shop in Boulder last Tuesday with a steel frame bike that had an aluminum seatpost completely seized. He watched me struggle with the penetrating oil and the bench vise for a bit, then just said, 'Try a bag of ice on the post and a heat gun on the tube, but not too hot.' I was skeptical, but the temperature difference broke it free in about ten minutes. Has anyone else had luck with that thermal shock method on different frame materials?
Be careful with that heat on a steel frame. You can ruin the paint or temper the metal if you get it too hot. A hair dryer is often enough to get the job done.