My garage contains several cans of sprays, lubricants, penetrants for various applications.  Last summer my friend who works on vintage motorcycles told me to get a can of Aerokroil when I was unsuccessfully trying to knock the slugs and jugs free on a locked up bike I had.  I had to hunt around to find Aerokroil and finally got it at a machine shop.  It's expensive at about 13 bucks a can (a smaller can than normal too.)  That's why I reserve it for only really tough jobs.  Also, we call it the 'cancer juice' assuming anything that penetrates rusted metal better than PB Blaster is going to give you cancer if you work around it long enough.  I make an effort to not get this onto my bare skin or get drips of it into my eyes/mouth/nose.  So here's the run down of commonly known penetrants on a scale of their effectiveness:  WD 40, Liquid Wrench, PB Blaster, Deep Creep, Aerokoil.  That list is in order by price too. I use WD 40 to keep things from developing surface rust and to clean grease off of motorcycle chains.  I no longer stock Liquid Wrench and use PB Blaster on nearly everything that's not rust welded.  I don't use Deep Creep because I don't need it now.  Aerokroil sits at the top of my known penetrants to free up things that lesser men will just snap off, break, or cut out with a torch.  If you are a long time PB Blaster fan, you should get some of this stuff to see just how much better it works.