As a safeguard, when buying a used gun try to get a gun doc to look at it first. I know this isn't very practical, but I sopose it could save you from a situation like this, assuming that the problem was present upon the sale of the gun. This is a lesson I learnt first hand, not trying to preach, I know exactly how you feel right now, and I know that it sucks. The only thing you can do is open her up, take a look inside and call it from there. If I were you I would look into finding a local gun doc, and have him open it. I opened my first gun myself, although I got lucky, I almost lost a few pieces and couldn't place them correctly. If you want to walk the path of doing it yourself, look up your gun on mechbox.com. They have some extremely useful videos on how to take apart and reassemble mechboxes.
Good Luck!!
EDIT: Just saw your last post, disregard the mechbox.com stuff
