Due to no pictures, I have to describe what happened. Yesterday I was tired of my driver's side mirror not staying in place after each time I shut the door, it would slip out of adjustment. So I unscrewed the mirror and just as the last screw was about out I heard a scary sound, a loud bang sound as a piece of metal fell to the bottom of the door from the inside. I thought, "What the heck was that, the backing plate to the rear view mirror!?? How did that happen, and what was it that happened?" Today I decide to begin the job of fixing whatever it was that happened. I took the door panel off. My year truck a 1974 C10 long bed doesn't have much of a inside door panel to begin with and it's all held on by a small handful of #8 11/8" chrome plated course thread screws, 4 screws near the bottom of the panel going horizontally along the panel, 2 in the arm rest and remove that, and 1 behind the door lever that sits in it's pocket at the top of the pocket. Unscrew the plastic door lock knob and remove, take the window crank handle off, mine doesn't have the wire clip holding it on the regulator window crank pin so I just wiggle it off. Pulling the door handle out and hold the handle out, lift the panel up over the door lock rod end and pull out on the front pulling the panel out off the window crank pin, and lifting up and out on the front of the panel, out of the window slit where the window glass is and off the door. There's a large opening on the left side where you can reach inside the door. Raise the window up all the way. Now, depending on the size of your arm you should be able to get your arm down into the bottom of the door and as far towards the front of the door as you can. I couldn't feel or with my finger move any loose piece of metal so I went and got a long screw driver to extend my reach. Then I found it and scooted it back towards the part of the door where I could get it and pulled it out. I had see it before when I rebuilt the doors, it was the backing plate for the screws to the rear view mirror. Oh, but here's where it got interesting, how to get it back where it belonged beneath and behind the vent window track and tightening mechanism. There is framing up near where it goes and a little bracket it sits behind that has a nut plate on it. "Where's the screw?" "Maybe it fell out and is in the bottom of the door." I went and got a telescoping magnet but I couldn't find anything but little bits of rust down at the front corner of the outside skin where the door corners are rusting. I struggled for nearly an hour trying every way I could to get that backing plate back up where it goes. At one point I even had the vent window nearly completely out to gain some space so I could get my baseball mitt size hands up into that very small space forward of the vent window framing and bracketry where that backing plate goes. But I couldn't raise the window and remove the vent window at the same time. I had to keep the window down and I couldn't put my hand inside the door like that. It was very frustrating to the max! I was at wits end so I sat down for a couple of minutes trying to calm down because I was not accepting that I might have to remove the window glass and the vent window just to get the backing plate back up there and put one small screw in it?? No way!! So, by God's strength I tried one more time to get that backing plate past the vent window track and up into the corner where the backing plate goes...with my finger tips holding on to it!! I got my rachet and the screw and fished the screw into all the holes it goes through and into the nut plate. On the inside door skin up there near the vent window are several holes and a rectangular shaped opening for something I haven't figured out, maybe to be able to adjust the spring at the front of the lower vent window frame which tightens or loosens the vent window as you swing it out, but the backing plate will not go through that opening, I tried. And there are a couple of different size holes there also, one of them IS for the backing plate screw that goes into a nut plate at the back of the bracket, that long screw must go to, as you pass it through the backing plate which has a hole for that screw to pass through as well at the same time. So there are three holes that screw must go through to fasten the backing plate to the door! I even dropped the rachet one time and nearly had a heart attack. But I finally got it without having to take everything out of the door just for one little screw. I put the rear view mirror back on the door and put the inside door panel back on and everything back together. Then it dawned on me, "I wonder if the other rear view mirror is like this, where the backing plate doesn't have the screw in it?" Because when I was looking for an acceptable screw I came across two of these screws that looked like they would go in that backing plate nut plate and bracket. "Where did the second one come from?" "Why would I have taken those screws out?" "Did I do it when I took the factory mirrors off, and the new mirrors didn't take a screw like that to attach them to the door?" Of course I'm gun shy now! I'll have to remove the door panel and look up in there to see if that backing plate is screwed to the door before I go taking the rear view mirror off the other side, I'll tell you that!