We're not communicating. Again, I know what the outer gasket/seal is. It's the black outer ring in your pic. What I am trying to describe is adhered to both sides of the t-stat inlet flange. I don't know how else to describe it.That's the thermostat "gasket" - it's a U-channel formed black rubber ring that can be removed from a new 'stat. Once squashed and heated/cooled a skrillion times the things turn to snot.
Funny you mention Sperry Gyro. My 89 year old father-in-law was a chief engineer there. He was on the team that designed the Sparrow missile. Designed a lot of global navigation systems before GPS.Black rubber covered center valve ????
That smacks of an old submarine engineering observation: "You know what an elephant is ??" ...... "No, What ?" ............ "A Sperry-developed mouse.". (Sperry Gyroscope could overbuild anything on earth)