yep, shellac...
Really really, Use sewing machine oil only. It is not a modern "miracle" cleaner that wipes the grunge of with a paper towel (none actually do anyway) but it will not cause any harm to the finish of the machine. Remember that your machine took decades to get gross, it's ok for it to take days or weeks to clean.
Another thing to remember about cleaning old machines is that if you try a spot here and then try a spot there, it will be more difficult than if you start in one corner, use gentle swirling motions and once you have a clean spot continue to work from your clean spot to the mess. the transition area where it is not quite clean and not quite gross is easier to work through then a fresh area. if you do that over the whole machine it will really clean up amazing well.