I don't know if Kroil oil will dissolve old grease but, on the Abused Free that I worked on recently, every rusted bolt/screw was removed after using Kroil. This oil is incredible and it may be hard to find. It is mainly sold to industry end users. It comes in aerosol spray and squirt cans. The aerosol with the tube attached is especially useful for getting into hard to reach places on machine innards. WD-40 can't touch this stuff. Hope this helps.
Soman2
The other Rodney