If it's something like hard water spots, then vinegar will most likely do the trick. If it's some crusty spots on the metal, then Semichrome should work. Tarnishy stuff? Nevrdull is the bomb for that. Tinfoil? Never tried that; I'll have to, one of these days. Always used Simichrome and Nevrdull on my bikes... but, if that guk's eaten into the metal? Then you're kinda screwed...
