3 in 1 oil "varnishes" over time,
I remember a Singer sewing machine serviceman tell my mother never use 3 in 1 oil on a sewing machine. It gums up the internals to the point nothing moves (also voids the warranty). The only way to clean it is to put the whole machine into a solvent tank.
Way oil should have a high "creep" value (wicking into cracks) and a high cling value. If you can't find any locally or if you run out, you can use "bar and chain" oil for a chain saw as a temporary substitute. It is what I am currently using.
I have used Mobil 1 10-30 in a pinch, Worked well but not sure of what long term effects of it would be.