Thanks a lot for the tips. I will try to find this square section gasket, and I will try to combine with the non hardening gasket sealer.
Air bubbles coming out were in the "just a few right away" category with the plug sealed a bit tight.
I am also thinking as a last effort to use the thread repair kit of permatex in case the insert has a crack somewhere. I read about this in the repair guide of the sB website.