I think I know what you're talking about. I just went back out in the garage and put one of the viton seals on my bare head and then got a 10 MM socket and my rubber mallet and tapped on the seal and it went down just SLIGHTLY more. Not much but enough I could tell.
We just pushed them on. They were tight too. Guess not tight enough.
FFFF looks like I'm pulling it apart this weekend again.