I’d give it another shot of sewing machine oil and let it set for a couple of days. If the BC is rusted onto the latch pin in the shuttle assembly, it may take a little while for the oil to wick inside. If you haven’t already, remove the needle plate so you can drizzle SM oil down into the bobbin case from the top. I had one on a 221 that come loose after an oil soak.
Can you post a photo of yours?
CD in Oklahoma