No, no, no, never oil the motor. Refer to the two links below.
http://www.featherweight221.com/fwrx/index.html
http://www.novamontgomery.com/featherweight-s.htm
Quote from the book, Featherweight 221, The Perfect Portable "Do not, under any circumstances, try to inject oil or anything similar into the motor's grease tubes. If you do, the oil will find its way onto the motor commutator or will saturate its brushes - they are made of carbon and must be kept bone dry for proper operation."
Order some Singer Motor Grease. Below are two links for you.
http://www.sew-classic.com/
http://www.april1930s.com/