Hi, Milton,
Are you saying that the base pin bushing rusted into the cylinder or that the base pin rusted into the bushing? The former is often not correctable, but you can get the cylinder out and the gun will work OK.
If the base pin is rusted into the frame or into the bushing, I can only suggest a long soak (days) in Kroil, then after removing the hammer and the base pin lock, try driving the base pin forward from the back with a brass punch. Use the Kroil, tap it, more soaking, try again, and so on. If it is stubborn, remove the ejector rod assembly so you can set the gun up in a vise in such a way that the front of the frame is supported while trying to drive out the base pin. Those frames are not very strong and you can bend or break them fairly easily.
Jim