against all rules

[harborrat]

I got some rusted up wrenches at an estate sale once and out of the four, only one was not seized up.  The working one I took to an antique shop and consigned it for sale as it had a wood handle and was marked Penn Central RR.  The other three I put in a bucket full of kerosene in the back corner under the workbench and forgot about them for two years.  After I rediscovered the ones in the bucket I found that only one had become movable with some work. So the foolproof method of soaking in kerosene for extended lengths of time does not always work either. 

[Papaw]

The working one I took to an antique shop and consigned it for sale as it had a wood handle and was marked Penn Central RR.

Did it sell? For how much and how long did it take to sell?

[harborrat]

They marked it for sale for $20.00 and it sold after several months.   I got about fourteen bucks after their commision.  I had bought the lot for about three dollars at the estate sale. 

[scottg]

Something nobody else has mentioned that has worked for me.........
Hoof nippers!
Adjustable wrenches usually have straight knurling on the little adjuster. If you try vise grips or anything else, you can kiss the knurling goodbye.
But an old hoof nipper has 2 knife edged jaws that bite right in between the knurling, and will grip well with no after evidence you were ever there.

Several days with penetrating oil before you even start. Patience is everything.
Then grip the little bastard and try to rock it.
If you can get it to move even slightly?? Even barely? You are in.
More oil and rock it.
  More oil, rock it.
More and more oil (its a sloppy messy job I tell you!) and just keep rocking. Each time a tiny bit further if you can, but watch you don't try to take too much in one bite.  It'll stick tight again.
Sooner or later (later, lets face it) it will loosen all the way up.   

If you can't get even that first hint of movement? More oil and try again tomorrow.
   Haste kills.
  Patience wins.
  yours Scott