Ed,
About 15 years ago I actually met the GE chemist that invented their brand  
of silicone sealant. In our discussion he said that it has been used for many  
things it was not intended for. He explained that they came up with silicone  
sealant as a means to create a seal between two objects that would have 
pressure  between them. Since then it has been used for everything from sealing 
bathtubs  and windows to automotive applications. The problem with silicone is 
that it  doesn't adhere well to some surfaces.
The one part urethane you mentioned is some of the stickiest crap I've ever  
used. Once it has cured, it is almost impervious to anything and it will last 
a  very long time.
 
Rummy



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