In my experience all cooling sytem o-rings don't seal after a while.
takes a few years .....but installed dry ...they don't last 'forever' .

I always use a high qualityblack silicone sealant.
Good stuff seals just fine metal-to-metal even, and many modern cars
don't even use gaskets or o-rings to seal things like a water pump or an
oil pan .
  I use the newo-ring, I just don't install it dry.

O-ring sealing is kinda dumb to me. AT first, they fill up the space
they're captured in ...
to the 'just right' degree of compression I'm sure and work very nicely.
but a few years later ...
the o-ring gets hard, or shrinks or something ....they can't work
really, really long term in my experience.
A problem with o-rings brought down the Space Shuttleeven.

scott
turbovans

On 12/1/2012 1:25 PM, Robert Clemmer wrote:
> Ok, today I finally got the water pump out.    UPS is scheduled for Monday
> delivery of the new one.  Not too much swearing.  I was surprised to find
> that it wasn't the pump shaft leaking even though it was noisy and a little
> loose, but the O-ring had become hard and lost its seal over the years.    A
> little clean up with the wire brush and I'll be ready to reassemble.  Oil
> pressure gauge will go in the same time while the engine tin is off.
>
>
>
> I think I read here where someone uses a little black silicone on the
> o-ring.  I curious about the pros and cons of using this.
>
>
>
> Bob C
>