Is this a steel spring having something to do with the hinged lid attaching? If so, I will be looking at mine this week too. I have a 500A I picked up a few weeks ago needing a lot of parts and grabbed a 503A in bad shape at the salvage shop today-knew it was there and would most likely have the parts I need.
You must be sewing machine blessed. You are finding, inheriting
and being gifted some great machines!