While I was waiting for hubby to wag home the chemicals from work I tried the sewing machine oil and it made some progress on the dirt. It wouldn't touch the brownish yellow gunk covering the decals. This machine has a lot of wear on the decals, especially on the bed.
Being very cautious of the decals, I tried some of the Dairy Du we use to cleanup our milking equipment. It is a powdered detergent designed to cut through milk fat. I have used it to cleanup some pretty icky vintage milk equipment.
I mixed up a batch in hot water and dabbed it on the gunk. It softened up the old oil, dirt, and lint, but stopped at the shellac. I started on the bottom and then tried the area over the decals on the treadle belt cover. I had excellent success on the really thick stiff using a frayed bamboo skewer and a very light touch over the decals. After I wiped the machine down with a nearly dry rag, I oiled it all over with the SM oil. It looks a lot better, and if I ever get my hubby to bring home the rest of the chemicals, I'll finish the process Glenn's way.
Just so you know there is another gunk buster out there that will help us clean up these beauties with out damaging them. (I would still not soak a japanned piece or an unprotected decal with it, just in case, as I haven't tested it on multiple machine surfaces.)