I had the same issue with my 2009 60 cm Sam in 2021. See photos below, where the separation actually led to a crack in the headtube. Rivendell agreed to repair it under warranty and sent it to Steve Rex i Sacramento to replace the headtube with, I believe, one with a slightly thicker wall. They then sent it D&D to match the green paint; but they ended up repainting the entire frame and then Riv agreed to send him the fork as well to match it since the green was not the same, so I now have effectively a brand new bike, the one I just took on our 3.5 week tour of Austria, Slovenia and northern Italy.
-Mike Cinibulk