Everyone has their favorite penetrating oil. I use some stuff that Primrose makes and I use their fuel conditioner as well. One of the things I do on bolts that are going to be a real pain if they break such as those in caged nuts is I plug weld a bigger nut to the head and then throw water on it. That breaks nearly all of them loose. If they break off, I plug weld a nut to the broken piece. I have never had one to break off so deep in the threads that I couldn't reach them with a wire welder. Its amazing what welding on a rusted bolt will do.
