You could try contact cleaner from an electronics store (like Radio-Shack). It's made specially for fixing stuff like that. It comes in a spray can with a little straw. No house should be without a bottle of the stuff. It lasts forever and will also fix the scratchy volume knob on your radio
Since WD40 is an oil, I would save it for last if nothing else works. You can spray it on a paper towel and wipe with the stuff. You can also protect regions with paper.
WD40 is a petroleum distillate and can take a long time to perfectly dry if not exposed to air. Never use it on shutter blades or an aperture diaphragm!
There is also something called Naval Jelly for really thick rust, which doesn't seem to be your case.
