If you have a manual, you can look at the oiling page, and it will tell you about the bobbin case, the rail and usually a pic of how this all goes together as well as where the oil goes.
I just purchased a White Rotary 1940's and it suggested that with the bobbin case out, place a small dot of oil on your fingertip and oil the case and the rail (inside where it fits). You might find that with just a touch of oil things will move better.