The rear view mirror fell off my 96 Z34 Monte Carlo. I don't see any kind of set screw to remove the mirror from the mounting plate. Anyone know the secret?

There is a small tube of special glue that is available for metal to glass and is available at any parts store. You have to remove the part that attaches to the glass using a small hex, apply the glue as per instructions and attach it to the glass. Both surfaces have to be clean before mounting.
You can even go to any Auto Glass shop and they will install it for you at a reasonable price. Good Luck.