The very best way to loosen rusted bolts/nuts is to heat the nut with a torch, red hot, and keep spraying it with water until it dools down. You may have to do this 2 or 3 times. Do this BEFORE you spray any anything else or it doesn't work as well. This works on tight fittings, pipe plugs or anything that can be safely heated & cooled. I guarantee you that this will be a very good way to get them loose. Use plenty of water in a spray bottle & try to get the water to work down into the threads- that is the trick- flood the heated item with a water spray so the water can get into the rusted threads. Try this first, and you can stop using anything else.Let me know what you think!