I agree with several mentioning the lemon law. It does sound suspect when they can't figure out where a spring came from.... I think that since the machine has a great warrantee, I would consider contacting the BabyLoc Company itself. I would express my frustration with the service of my local--or not so local--dealer.
I know I have shared my machine woes on this site as well. Best of luck! Hope you can get satisfaction so you are not using up all that wonderful sewing energy in frustration!