Mineral spirits or naphtha both work well.
I have heard of people using kerosene to soak, or gasoline when kerosene just doesn't cut it.
Advise you to blow the parts off with an air compressor. These solvents are very flammable. If you do not have an air compressor I would just leave them somewhere sunny or warm. Use these solvents outside so your house doesn't smell like solvent.