I didn't read every reponse but.
Soak in the blaster or whatever for a couple days.
wipe out excess.
Use your homemade tool on and impact driver.
Type you hit with a hammer.
If that don't work.
Use a mini micro torch.
Heat only the cylinder all the way around the nipple.
Don't heat the nipple itself.
Now use the impact.
It should break loose.