This motor and gear lube from the Featherweight Shop is what we are now using in our shop and classes. We have tested this against the Singer branded lube and the popular synthetic grease on the market and have found this to be the best product for your vintage sewing machine.
The tip of the Syringe fits down inside the motor lube tubes and makes it real easy to fill them. This lube also works great on the potted motors on Singer 15-91's, 201-2, and others.
This lube does an excellent job on the gears as well, offering low-drag lubrication and very good adherence under high speed such as on the Singer 301s.