That'll kill it for sure. The keyboard is a couple of slices of conductive rubber-like material that are squeezed together to make a connection when you press a key and it bears down on the material. Petroleum products like WD40 will, at a minimum, just gum up the works; and might attack the synthetic rubber membranes.

If you're limited to common household chemicals, try rubbing (isopropyl) alcohol. If you can take the time to go to Radio Shack, buy a can of contact cleaner spray as Tom recommends.

My old HP41 exhibits sticky keys too. So far I haven't had to open it up and try cleaning it--good because I give it only 50-50 odds of working/killing it for sure--but I've found that pressing a particularly sticky key hard a few times clears it up.