One of my backs (120) for my RB67 has an annoying habit of not "recognizing" that a shot has been taken. As a result, you can't advance the film. I figured out that I can work around it by taking the back off of the camera, and then poking a small pin into one of the holes on the top of the back. You can hear something inside "triggering" when you do that. From what I can tell, the camera body has a small rod that is supposed to poke that for you, but apparently this one is off some how. Is there an easy fix for this? Is it worth pulling it apart to see...what?