hamcereal

Yeah I've exhausted the non destructive options, I had used the seat post clamp to clamp a 3ft. breaker bar and tried to turn, but I snapped the clamp bolts ☹️

madpogue 

Did you try this?

In fact, I would redact the "if all else fails" part. I would do the solvent / rust-breaker option via the BB shell fairly early on in the process. If you've only done the solvent attempt from the top, try this next.

3alarmer 

.
...if, indeed, your seat post is sized correctly, and it's simply seized due to galvanic corrosion, a lot of the problem occurs in these cases because of the length of the seat post inserted in the seat tube. A 12 or 14 inch length of post inserted fully into a tube without grease or anti-seize gives a significant surface area for bonding. Before I started using the torch/penetrating oil method on these, I worked on a lot of them for people who brought them into the bike co-op here,

We used the giant bench vise there to grab the post, then two guys grab the frame, one twisting it up and down, the other leaning backwards and pulling, to remove them. I once ripped the seat tube lug open on some guy's frame, because the thing started twisting, but it was still bonded by the corrosion inside the lug. I felt bad about that, but it was junk with the stuck post anyway.

This is all by way of saying that you might need to get that ATF or Freeze Off down into a considerable length of tight space before this breaks free. The heating and cooling helps with that. When you get it out, you might want to consider shortening it with a saw and a file or grinder to finish taper the cut end. I pretty much do that routinely now, but I also use anti-seize.

madpogue 

Another reason to apply the solvent approach via the BB shell as well as from above.