Sheila,
I have many old tubes of the Singer motor lube. I still use them in the Singer motors. However Singer no longer makes the motor lube. All they sell now is a gear lube, not suitable to motors.
Not too long ago in another thread someone made a post where they linked to a blog I believe where the blogger commented that the Singer motor lube and petroleum jelly were indistinguishable. I have done a wee bit of comparison and for the most part this is true. The Singer lube seems to be a bit thicker, but has the same consistency.
So, that I why I said if you don't have the Singer lube use the petroleum jelly.
Joe