They're almost always missing on Featherweights at Estate Sales. You can get up to $50.00 for an original featherweight bobbin case, so they usually get stolen. Any time I see a featherweight on an estate sale site, I email the estate agent/seller and tell them to remove the bobbin case. Given they don't deal with them every day, they don't know, but it will get stolen if left in the machine.
bkay