Not much to add, except that waiting overnight, after having drenched the thing in your elixir of choice, sometimes does the trick. After the elixir, you can lightly/sharply tappety-tap-tap with a plastic hammer if you like. That can crack the dried oil enough to let the elixer penetrate. Maybe try a soft (not beryllium) copper hammer, if you're feeling intrepid. At some point, I would get out my channel locks, wrap the inner knob with shoe leather, and give it a good twist, back-and-forth style. Only do this, though, if you've got experience mechanicing stuff. Over time you get a sense for how to use heavier tools (and oxy-acetylene torches) with a light touch. The good news: they Always come loose. They shrug their little steel shoulders and give up the fight.
FWIW, I've never had kero (or wd40 for that matter) hurt a finish on a sewing machine, though I always test, every time: I mix in a little huile-du-jour (Miracle Mystery is good, and minty) and pour it on. You're gonna clean the thing up anyway, aren't ya?
PS: Tappety-tap only on plated surfaces: painted surfaces will chip, even under the gentle ministrations of a wedding ring!
Last edited by QuiltnNan; 01-01-2018 at 11:06 AM.
Reason: remove shouting/all caps