OLD, ANCIENT, DRIED, SOLIDIFIED oil. When that machine was made sewing machine oils were sometimes made from sperm whales. And those that were not were no where near as well refined as what we have available today. Also many of these machines made it through the great depression as the only machine a family(s) had. To keep it working they'd use any oil they could find. Even old coal oil or the dregs from the crankcase of the family jalopy. As long as the oil was fresh it's ok, but once the machine was retired that oil solidified. Especially when exposed to heat, and dry air.
I had one Singer 127 that was so bad like you described that oils and kerosene wouldn't touch it. I had to use Hoppe's #9 Gun solvent to clean the majority of it off. Then under the bottom I used denatured alcohol on the rods and other pieces to finish it. I did not use anything but oils on the top.
As far as alcohol, or acetone, or any other of the nasty solvents .... don't use 'em.
Joe