We're jinxing ourselves even talking about this stuff. This discussion alone causes leaks. It's not good to talk about it.

I've only used the ones from old MP kits and Fel Pro kits.

They have all had a number molded into them: 4227926. I had to look really closely to see it.....(It's not hard to guess whos tooling they came from).

Avoiding snafus during install + the side seals seem to cause alot of problems.

Though the white "swells up when soaked in mineral spirits" side seals never really
gave me any trouble, I always thought they were a pain to install and I used up my last pair several years ago on a 440 re-ring.
don't believe they are made anymore (were they asbestos or something?).

So on a modern build, myself I substitute RTV for the side seals. I try to inject it inside the groove
as much as possible and also pack that area using putty knife/fingers and so on.