What causes the rear view mirror liquid to disappear from part of the mirror when there is no leakage around the mirror glass?  Is this an age thing?  Is there a way to keep this from happening?
I purchased the car with this problem in the mirror so I replaced the mirror with one from the salvage yard. One month later I now have the same problem.
	
		
			
		
		
	
				
			I purchased the car with this problem in the mirror so I replaced the mirror with one from the salvage yard. One month later I now have the same problem.
 
	