Originally Posted by Nectaris
The ones with an oring are made to help prevent it from loosening. You won't want to use those without the oring.
I've had a case where the o ring prevented the detent from reaching into the breach far enough to do it's job, but also without it was too far into the breach.
Just depends on your situation, wgp made bodies with different wall thicknesses and aftermarket companies don't always test their detents on all bodies.
Part of owning a cocker is problem solving