Perlick Faucet Drips

So I finished my Keezer and currently have 2 taps. I'm using the stainless perlick 525s. One works perfectly, but I can't get it to stop dripping. There's a very slow drip coming from the connection between the faucet and the shank, where those teeth fit together. Comparing the two faucets, the one that works slides into place a bit further, the teeth aren't visible when looking at the connection from the side (perpendicular). The one that leaks just doesn't seem to slide all the way in. Both have the rubber rings set in behind the teeth on the faucet. Other than pushing harder or fiddling with the rubber ring, any idea what I can do?

This probably isn't the kind of problem that someone can just say "just do this..." but i don't know. Has anyone had trouble like this before?

Swap the 2 faucets and then let us know if the problem follows the faucet or stays with the shank. It sounds like the shank might not be machined properly.

The first version of the Perlick forward seal faucet had the problem in spades. The new ones are ok.