Disassemble, then work with a toothbrush and kerosene, turpentine, or any other solvent.
Gasoline is dangerous as fumes are heavier than air and any ignition source or spark will ignite them. Every year we get a flamer or two when someone here tries to clean something in their basement with gasoline and the hot water heater pilot gets involved. (I'm off my soapbox, now!)
If you have several mags or the cosmo has really hardened on, you can let them soak overnight in a solvent filled baking pan.
Lots of way to do this; some are more labor intensive than others!