Remote control mirror mounting

Have a question on how the remote control mirror on a 73 GTS mounts to the door panel.  I think I am missing a backing plate/retainer piece.  All I have is the control and the bezel that screws onto it on the interior side of the panel but nothing to secure it on the back side of the panel when I screw the bezel on.  Would like to know what I am missing and what it looks like so I can start going through my miscellaneous leftover pieces.  thanks. -  dave

Vince, I do have sport panels.  I found a couple of pictures on ebay, one shows a nylon looking washer and  the other one shows a metal washer that sits on the backside.  It makes sense but when I got the mirror out of the baggie it was in there wasn't a washer.  Like you said I'll wait and see if anyone has the answer but I'll probably play with it tomorrow and see what I can come up with.  thanks - dave

That I don't have, have to see if I can come up with a substitute.  Thanks for the pic.

 sorry, late to the party... yes its a thin sheet metal type washer. they get lost easily 

Just a little follow-up on this, while I was looking for some self tapping bolts for mounting my back seat I was going through a box I have with a lot of the old bolts and nuts from the car when it was torn apart, I came across the "missing" washer.  Of course this was after I had already ordered a new one.  Pretty typical for me.....