Mirror glass

Hi I have just purchased a 1987 W126 300SE in the UK and am delighted with it. There is a small rectangular mirror glass stuck onto the shaped glass on the offside driving exterior mirror/ I imagine the PO didn't want the expense of replacing the actual mirror glass at some time. It works OK but it is now a distraction to me. Question is how do I remove the glass to replace it. I imagine it levers off some kind of central clip but I don't want to damage the mirror body. Any advice appreciated. Thanks Jim