Quoted from Singer 221-1 manual dated 1-48.
To Oil the Machine
Page 24:
To insure easy running, the machine require oiling and if used continuously it should be oiled each day. With moderate use, an occasional oiling is sufficient.
Page 27:
USE ONLY "SINGER" MOTOR LUBRICANT FOR LUBRICATING THE MOTOR. A tube of this lubricant is sent with the machine.
The SINGER Motor Lubricant is a specially prepared non-flowing compound which is not affected by varying temperatures. It is the only lubricant which will positively lubricate the motor. Other lubricants, including oil, vaseline or ordinary grease must not be used for lubricating the motor as they are harmful for this purpose.
When the machine is shipped from the factory, the two motor grease tubes (A, Fig. 27) are filled with sufficient SINGER Motor Lubricant for approximately six months of use, under ordinary circumstances.
At least once every six months thereafter, these grease tubes should be refilled with the SINGER Motor Lubricant. <snip>
Well, perhaps my manual is written differently, but these instructions seem fairly clear to me.
And to the best of my typing ability the above is a direct word for word quote from the manual.
Joe