Now and then you will find that a nut or bolt simply will not undo. You have tried everything: heat, penetrating oil and even an impact wrench but still the fastener remains resolutely tight. There is one more thing before you reach for the angle grinder. It definitely does have a normal right-hand thread of course? Sometimes left-hand threads are used to prevent fasteners from undoing in normal use. These are almost always found on rotating parts, such as engine or transmission components or possibly on the wheels.
Candidate for rusty nuts!
It you have wire wheels and have just bought a tyre you may see on the side the word Tubeless. This does not mean that you do not need an inner tube, nor does it mean that you cannot use an inner tube. This indicates that no tube is necessary provided that you have wheels which are suitable. Unless you have special rims with external mounting points for the spokes, your wheels are not suitable and air will escape.
If you have difficulty in removing a fork leg, what is probably happening is that the lower yoke clamp is doing its job, so tap in a suitable wedge to open up the gap. Often the assembly will start to descend quite suddenly, but with luck your strategically placed foot will prevent any damage — to the fork leg, that is. Steel toe caps?