Heat will work but try this. Get snobol and soak the end in it. I was helping a friend with a mast step that was corroded. I pulled out some snobol and soaked the part in in for a few hours and when we pulled it out it was like new. It removed all of it.

I was joking around with him when we went back to look at it and before he could see it I told him the part had been disolved completely. Had him going for a sec.