This is a 69 mirror. I soaked it mirror down in acetone over night and it was still tight. Mine had a black silicone like material on it and acetone didn't do much. Glass was a bear to remove. I guess this silicone material isn't as common as the other adhesive they used. The regular stuff should loosen right up. Drill out 2 rivets and your good. Just be careful removing mirror, you will know if it's still tight. Heartbeat city does sell dated mirrors if you break it.
