Use a heat gun (or your wifes hair dryer) to warm up the metal around the filler neck and the filler neck itself. Is it a metal cap? I can’t recall what they use. If its a metal cap, you don’t have to worry about controlling the heat so much. Get the filler neck good and hot and using your tools to protect the knurl it should come out.
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...