Amazing that they didn't put in the manual whether or not to oil. I searched online and found several instances where people were asking the same question you are, all saying that they had been told that the machine did not need oiling, but questioning whether that was really the case. Since your machine is running smoothly (which is indeed remarkable for a machine that hasn't been used in so long) I would clean it and then not worry about oiling. You should also be able to call a Singer repair place and verify that it doesn't need oil.