Before going to the trouble of removing the ignition in any manner, you should concentrate on getting the key out. Once removed, proper lubricant can be applied to it and sprayed into the lock. Do not use something like WD-40 or anything petroleum based, it will just collect dirt and gum things up worse. Use powdered graphite or a lubricant designed for locks such as Houdini.
The mechanics behind the bumping out of the key consist of a spring loaded ball and a chisel point tab. They sit in a dead end that cannot be directly lubricated without complete disassembly. I have never tried, but without complete disassembly perhaps soaking the entire unit in a solvent such as lacquer thinner or acetone might free things up enough to give some more years of service.
good luck
Larry