Don't forget the old torch! It lets the lube seep in farther by expanding the gap.
somestimes a slight turn in the oppiste direction you are trying to losen depending on left or right hand thread along with penetratring oil can crack the rusty boltWD40 always help.
i used to work next to a machine shop that specialized in rehabbing rendering plant equipment (they cook animals into goo to make stuff with it, was a NASTY place) the old machinist that worked there gave me a pint of a silvery black goo in an unmarked can, i know its not never seize, i think it was a mix of graphite, lead and some kind of grease, he told me it was his "special stuff" and if i ever planned on taking somethings apart use it, at the time i was working on heavy equipment, trash trucks, bulldozers, track hoes, pans ect all dirty disgusting things. every thing i ever put it on came right apart with out issue, now i use it very sparingly on break drums bearing hubs and the backs of alloy wheels, every wheel i have ever put it on fell right off, my other mechanic refuses to use it and is constantly having to beat on wheels to get them to come off, it doesn't take much just a few dabs with an acid brush and a smear around.Well not so much on freeing rust bolts but putting a compound on them so they always come free.
My father used to work in a foundry. The problem they had is if metal is heated and cooled continously the threads become corroded just the same as exhaust threads. They found that applying a mixture of graphite and oil always made the threads easy to remove. Its easy to apply because the oil makes it a paste, the oil does burn off but it leaves the graphite behind.
He had an old VW camper 1968 and he was always fitted exhaust systems due to corrosion. He decided to buy a stainless system so it would last longer, he coated the threads with the compound. Many years later it needed changing again due to the parts that weren't stainless corroding. The nuts holding the exhaust to the cylinder head had corroded with no signs of flats on them. A light grip with moile grips and they came of and the compound could still be seen on the threads. This is a good tip if you keep cars for many many years. I've applied it to my car though the turbo nuts and bolts aren't easy to access.
i think your right, its some kind of animal fat because it wont wash off with thinner, what was cooler than that grinder on dirty jobs was the gigantic container the machine shop had that was full of liquid lye, they would soak the equipment in it before working on it. they also had a lathe that had a chuck on it that was about 3ft in diameter and had a bed that was every bit of 20ft long, every time i saw it i was amazed, it was so huge when they closed up shop they just left it there it was assembled in placeThe Fezman, it's probably made from the stuff he scraped off the rendering equipment, literally elbow grease...errr... hoof grease? I saw an episode of Dirty Jobs where he put basically a whole cow into the grinder. Not some place you want to fall into.