There has been much discussion on this. The problem is the aluminum alloy reacting to steel. PB Blaster is no good for this. Industrial strength ammonia (10%) down the seat tube from the bottom bracket and lots of patience. I had one that took 10 days of soaking. I would tap the tube with a hammer using a hardwood block everyday. Patience is the key. The bond is very strong, and the ammonia will only penetrate a little bit every day. It can take weeks. Seat post in a vise and frame as leverage is the way to go. In my case, I had a seat post with a rail cradle on it, and put a sacrificial seat on, wedged it in a tree trunk and twisted. Move it a millimeter, and you can move it a mile. The other option is to saw it out with a hacksaw blade.