The methods posted above are all satisfactory, but, the finish on an older gun such as this won't take very intense cleaning, or very much of it. The problem you are trying to avoid is an "overcleaned" appearance, and I think you would get just that with any method listed above.
Try this. Stop in at at a hardware store and purchase a bottle of lemon oil furniture polish. The label may say lemon grass oil, but it is the same thing. Put just a touch of water on a white cloth of some sort, and put the oil on top of that-the water keeps the oil "up" on the cloth, rather than soaking into the rag and your hands. Gently work the cloth over all wood surfaces, I prefer to have the wood off the gun when I do this. Allow to stand someplace warm (not hot) for a day or two-a sunny corner of the room is excellent. The sun/warmth will bring some of the dark lubrication and sweat/oil out of the head and checkering areas. Repeat this process a few times until you are satisfied. You can use a lemon oil dampened toothbrush to work the checkering as well, if it is really grimy. After the last application, allow to stand a few days, and finish with your favorite, true oil or tung of some sort are both excellent.
Best,
Ted
