vorrange
Vapor.wise
There are a couple of things you can try. The power socket threads can become clogged with wood sap/sugar. There is a better chance of removing the power socket while it is hot. Try removing it right after unplugging.
As moisture leaves the wood from heating, it will shrink in all dimensions. This can cause the threads to hold the power socket tighter. If you leave the HI unplugged and in a very humid location, the wood will draw in moisture and swell in size. This will also make the old style core very loose and should make the power socket easier to remove as well.
Hope you have good luck getting it out so you can install a replacement element.
Thank you Alan. I thought of trying while hot, i'll give it a go and report back.