You know...from the time I bought my '95 back in January '06, over time, there seemed to be more and more of a slight vibration of the mirror that drove me nuts going down the road. Not enough that you could pull on it and it even feel loose, but SOMETHING. Got worse with heat, and one summer day just fell off the windshield.
After a cleaning and re-glue, all was rock steady--so it must have just been a partial weakening of the glue in spots that caused it.
Then again, now it's been cold for a while, and I'm starting to notice a hint of vibration in it again going down the road, so maybe the glue is once again getting weak. We'll see.