The stitch selectors will come loose with oiling. It's seriously worth picking up. It's not referred to as "the best machine Singer ever made" for nothing. Yes, a 401 takes cams, or uses the stitch selector, and if you want to get really fancy, you can use them together.
This is a post from my blog about a 401 I resurrected. The main shaft didn't turn, the stitch selectors didn't work, the throat plate didn't move, it had been peed on, in a fire, etc etc. It's in full working order now, and 90% of that was thanks to TriFlow oil, and a little elbow grease.
http://www.archaicarcane.com/2013/01...e-a-day-makes/