As far as I know there is not a viton version of this o-ring.  I haven't
really had a problem with it leaking as long as it is the newer version
and the nut holding the cooler in place is tight.  I tried running
synthetic on my 90 Carat motor and I never really noticed any advantage
in mileage, etc. so I switched back.  I just can't bring myself to
extend the oil changes :-)

--
Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: 856-327-4936
Fax: 856-327-2242

On 5/25/2011 10:40 PM, Max Wellhouse wrote:
> FWIW, I had been running Mobil 1 in the engine since  5k after its
> rebirth, but I've had several instances where the Oring seal  at the
> oil cooler was leaking.  It was doing it again last winter and into
> the spring, until I changed oil and returned to Castol High mileage
> 10/40 oil.  The leak, if not totally stopped, is much, much less for
> sure.
>
> Since the O ring seal is black and presumably not Viton, and since
> full synthetics love/demand Viton seals, could this be a coincidence,
> or something more??
>
> Does such a thing as a Viton Oil cooler seal exist??  An argument
> could be made that the oil filter seal is not Viton and normally
> doesn't leak, but I am at a loss to explain this in another logical
> fashion.
>
> TIA
>
> DM&FS
>