Half the job is tracking down repalcement parts. I have had good luck searching on ebay, contacting various sources like Helen Howes in the UK and individuals in the Treadle.on.network. On the
Victorian Sweatshop forum is a few clever people who knows this model first hand. I'm sure they can give more advice. I found
this face plate during a quick search on ebay, it looks like the spring is intact. I have no idea how Singer's version differs unfortunately. Keep and eye out and have patience and a replacement part will turn up.