Welcome Shannon! The melting temperature of the grease is important. It needs to be fairly low and most modern greases melt at a higher temperature than the old ones used in sewing machines. Vaseline melts at roughly the same temperature as the old greases that were used. Nova Montgomery sells a grease that is supposed to have the same properties as the old Singer motor lube.
http://www.novamontgomery.com/module...hSubmit=Search
I haven't used it so can't say for certain how good it is.
Rodney