Here are some links to how to clean up your machine:
https://archaicarcane.com/stuck-in-t...lant-o-matics/
Here's another:
Singer 403a
Some of these have further links that may be helpful. The only differences between the 400 series and 500 series is looks, so what applies to one also applies to the other. The other main differences are whether they have a built in camstack, which means they can sew zigzag patterns without putting a cam in the machine.
bkay