I have removed a stuck seatpost by all means described except those which suggest "dissolving" the seatpost. This made me stop and think as I bath aluminum parts in a caustic soda bath prior to anodizing. Leaving said parts in this bath too long very effectively eats too much of the aluminium away, rendering close tolerance parts unusable. "Red Devil" drain cleaner is nothing more than caustic soda; I use an 1/8 cup per liter or water and anything over 30 minutes is guaranteed to ruin the part. Use outside or in a well ventilated area as the fumes are toxic.
Sam Smith
Knoxville, TN