Bette,
I don't know anything about this "lint pin" thing either. I've got two 500a's so I'll take them down and see what I can see. If I can figure something out, I'll report back.
Both my 500s had to have the spring that holds the bobbin case in adjusted. There is a specification with tolerances in the service manual for it. One of mine was too loose, the other two tight. The tight one would sew along nicely then suddenly the thread would seem to catch on something and jam up wrapping itself around the bobbin assembly. After adjusting them to be within the specs I have no trouble with them.
I can't say that is the problem with your machine, but it's the only thing that I've had problems with in the 500 bobbin area.
Joe