All Small Six Weber 32/36 rough idle

[DON]

You are more computer competent than me for sure!!
I can see your area and why it’s not sealing around the elongated hole.
What I am seeing is the vacuum comes from inside the throat ( in red ). And you can see where the barrel has made an impression in the gasket just outside of the barrel- sealing the vacuum in the throat. (Black arrow). There should be no vacuum around the bolt holes. Sealing around the bolt holes should not be necessary.

 

[DON]

Correction, I am wrong, the gasket with the open center WOULD allow vacuum around the bolt hole

 

[63 Sprint]

Correct

 

[63 Sprint]

A simple fix would be an 1/8” aluminum plate fabricated exactly to the original Weber 32/36 spacer plate. Then use two properly sized gaskets to sandwich the plate between both gaskets.