Was using the 5D withg 70-200 L 2.8 yesterday morning when suddenly the viewfinder went black.....upon inspection after the lens was removed, the mirror and a piece of plactic about the size of the mirror droppe out....heard this happened before to a few other CSer...but am wondering if there are many such occurrence.....question is - how reliable is 5D if this happans often? ....imagine if you were using it for an event without backup when this happened.