Quick update. I took my MS to the local SC to take care of some issues and pointed out the panel gap between the headliner and C-pillar. My service advisor guessed that it was a broken/missing clip but when I told him that I personally installed a replacement clip he suggested that the plastic chassis behind the pillar is slightly misaligned and needed to be set a couple of millimeters higher. It took them 30 minutes to address the problem and now there is not gap between the headliner and the pillar. Looks like it's a relatively easy and minor defect that can be addressed by the service center.Thanks so much for the info, much appreciated.