Repeated from the Oiling page:
Oiling the key mechanism
Please, please do this once of twice per year. One doesn't use bore oil for this! Any light oil will do, like 3-in-1 oil, or sewing machine oil. I like to use a blunt syringe for getting into tight places. (Computer printer re-inking kits often include these.) Oil the keys in the crack between the post and the key, wherever they move. This not only keeps the keys moving freely, but it also prevents the screws from getting rusty and stuck.
I now use Doctor Syntek. See information under the Oiling page.