Looking at the image of this vapouriser is the part indicated part of the original or as I suspect a repair that has been made at some time.
That part is the spigot from the Tilley burner and the two spacers which are located below the spigot do not belong there either.
Thanks all, I managed to tease it off using WD40 and surprisingly it threads in to the gallery I thought the threads would be too damaged. I bought this (and others) about 25 years ago and just getting around to spending some time to clean them up.