Well it might leak if- as I said a while ago- if you have a misaligned oring in there, or a damaged collet, or a damaged oring, or some debris.
Popping off the collet isn't a big deal. A couple flat head screwdrivers applied under the collet will do it. Since you've eliminated so many other possibilities, I reckon it's worth having a look under there.
Oh.. the other thing I used to remove the orings when I found my access to the crochet (thanks
@tomcat59alan ) needles cut off was a bent paperclip. Straighten out a couple sides of one and then use a pair of pliers to bend the last 4 or so mm at the end into a hook. Works a treat. I don't care about whether they're metal or plastic or whatever because I'll discard the orings after removal anyways, but maybe that's just me.