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I have a vintage brass B & L Microscope. The mirror has what appears to be rust spots under the glass which cannot be removed. I have secured a replacement mirror(concave and Flat). I damaged the edge of the old mirror removing it from the holder, as the holder was so difficult to spread apart. I know there has to be a better way to spread the holder to accept the new mirror, without causing damage to the mirror. Does anyone know the correct way to install a replacement mirror on my microscope? Please advise.

NOTE: Am I in the wrong section of Microscope Forums, to secure an answer to my microscope problem?