Update: As I said, Made a gasket years ago for new type "tube" w/ cork and RTV... Finally failed. The cork w/ RTV sealer never compressed the cork and sealer can't survive 15psi and fail sooner or later. Sorry, No Pics because no time to take them.

Made a new casket out of thickest Permatex "tar paper" material. This is a bit thicker then depth of wide groove where old "rubber" lived.
The new casket compresses a bit when mounted. I used High Tack sealer to hold it to the "tube." (Would like to use Super 300 or Aviation sealer but didn't have it and no car to get.)

I pressure tested w/ Stant ST270 tester (update version of st255 ACdelco etc. low clearance tester.) then drive ~ 2 hours and seem to work and w/o hours to days for RTV to setup.
I used same method to replace casket for 87+ belt tension part where mounted over unused WP hole in the block that last 15+ years.

quote Originally posted by 2.5: Best way to avoid a leak is sealer

Often will fail w/ old type "tube" and w/ or w/o paper gasket used for them.
Old "tube" flange is weak and flex enough to break the seal.
even w/o that, RTV needs perfect cleaning to "glue" the surfaces. Poor cleaning = leaks. Many times more so if whatever behind it sees > 1PSI. If a gap is > a fraction of 1mm likely will fail sealing any PSI.
RTV has a gap filler only work for things w/o pressure like timing cover to pan on Duke engines. Even then needs prefect cleaning.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
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[This message has been edited by theogre (edited 08-17-2021).]