The white corrosion is on mine too. It looks similar to the corrosion on the anodes (I think they're called) on the bottom of the boat motor. Looks like a dis-similar metal issue. I clean it with some light weight oil and also put a drop or two into the hole and work the key in and out a few times to free it up.
To keep the key working easily, I also open the cap and place a drop or two on the two locking cogs. Then I rotate the key a few times to work the oil into the mechanism. Do that about every month or two and you'll have no problems.