I would suggest that, if you've cleaned it and lubricated it quite well, it may be time to take it to a gunsmith and have the action torn down and examined. Sounds like it's had a hard life, and there's no telling what kind of crud has built up inside the receiver over the years. If you're real handy with tools, you may be able to take it apart, clean it up, and reassemble it; but you do have to know what you're doing and what you're looking at once you've got it apart!