I saw a very rough looking 501A In a junk shop up the street. It was filthy in and out and had broken hinges on the doors. No attachments were with it. I was so surprised to find pristine white thread in the bobbin amid all that dust and dirt. My question is should I go back? It was marked 55 dollars. What exactly do the drop in cams do. are they hard to find? I want a machine I can use not one that there is no hope for.