singerguy,
I don't have a replacement bobbin case, but here's a tip. For machines like yours that defy normal cleaners I use Hoppe's #9 Gun Cleaning solvent. Works like a charm. Won't, or hasn't yet, damaged the finishes on any of the older black Singers I've used it on. You'll still need a brush but a tooth brush will do. Cotton balls and q-tips too. After that you can use denatured alcohol to remove the residue then oil it.
Joe