Man, that is one seriously locked in sucker.

It just occurred to me you could use a shop press if you have acccess, same as with the hammer but a wooden block on top.

If you do the impact wrench it has to be supported well, what makes an impact work in that case if no movement of the object.

Wooden boards and squeeze it in the vice using the handle as the counter to torque.

Heat may discolor the finish but at that point its what the heck. I would think the older blue vs the new not so shiny would be more at risk, that's a guess.

I might be temped to use a sledge hammer with a good block over the top.

Also possible to break the hex wrench thought its a good sized one. Pretty cheap.

The adaptor for the hex on the impact is gong to cost a bit.