I doubt I have anything special to add, though once I bought an air impact I couldn’t figure out why I’d waited so long to do it. Its not that it does everything, but it works wonders on many things I used to wrestle with. Impact of some kind is always my favorite approach. If I can’t fit the air tool I find a way to at least whack the wrench or socket with a heavy hammer - poor man’s impact.
Along with that goes the PB Blaster and, of course, heating. I’ve recently added cooling to that. So I’ll heat it up a whole lot. Then I turn one of those compressed air cans upside down and blast with that that. A couple cycles of that with some PB Blaster loosened up a broken head bolt for me quite nicely when I needed it to. After a bit of that the rest of the bolt came out with a pair of channel lock pliers. I’ve also done other normal things like pounded the next smaller size socket onto a bolt head (I prefer 12pts for that) or cut a slot in a stripped phillips head to get a grab with a flat blade…stuff like that.
My only real “failure” so far was an axle nut. I broke a 1/2" breaker bar on it while jumping up and down on an added 4 or 5ft cheater pipe. I finally put the tire back on and drove it to a shop I use. I asked them to break it loose & snug it back up so I could drive it home. My shade tree air tools are handy - but no match for the professional shop.
Tester - you need to move out of Minnesota or wherever it is. No one should have to deal with that much rust on a regular basis. Arizona’s much nicer on mechanics I’ll bet.