there is an amazing product from Wurth called rost-off ice which super cools and it really works on stuck posts. I used it many times in the shop and sometimes two of us would be pulling and twisting with the post in the vice and would eventually get it out. We save a very special custom quintana roo Tri bike with 650 wheels for a food customer... I was one of the hardest I have done. I did the cut an split once and I'll never do it again. You can get the post out with the right product and right tools.