I bought a new bike second-hand recently and it's in good shape, but I wanted to get the rear cogs back to their true, shiny selves. I tried scrubbing them with Goo Gone and a tooth brush, but only the teeth broke free of the many layers of blackened, dried grease. A lot of people on here seem to recommend kerosene - will that do the trick? Or should I give up on this admittedly obsessive enterprise?