Okay so here’s the situation, pictured above in the red circle is a nut, I need to get it off the bolt it’s on. it has likely been threaded on for 2 decades at the very minimum. The bolt it’s on has a perfectly flat round head that is currently spinning freely and has some play in it. There doesn’t look to be any serious corrosion. I have very little access to the bolt side and have to come from the viewing angle but can reach my fingers in and around the bolt and put pressure on it but won’t be able to get and serious tools back and around on the bolt side even if it wasn’t flat and round. The bolt and nut go through 2 small brackets that are coincident and are pinned together by the nut and bolt, and are only just wide enough to accommodate the nut and bolt fully.
I’m aware I could just come and Dremel the bolt off, replace the hardware when I put things back together and be done with it, however I’m trying to keep things as original as possible so decided I’d get some suggestions before biting the bullet and going with the nuclear option.