99 Regal rear view mirror - fluid behind the glass

A friend's rear view mirror came loose from the windshield of her 99 Regal. I helped her clean the windshield surface and re-attach the
wedge mount and mirror, but her mirror now looks like some fluid is between the glass and reflective surface. I presume this fluid plays some part in the auto-dimming mechanism. As far as we know, the mirror didn't strike the windshield when it fell, as it happened during the middle of the night. It was found the next morning hanging by the wires. Now, the mirror looks like it has an oily smear across parts of it which cannot be cleaned. Is this mirror now hosed, or is there any hope of restoring it? And to satisfy my own curiosity, what is this fluid, how did it get between the glass and reflective surface, and how does it work with the auto-dimming feature?
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