If the WD-40 isn't working try something a little more ambitious like PB Blaster. Spray a little on then tap the parts quickly and lightly. It seems to help the penetrating oil ... well, penetrate. I'll second the mineral oil and scotchbright pads for getting surface rust off too. Start with a brass wire brush and steel wool if it's really stubborn.

This must have been an exciting package to see over at the customs office.