I couldn't contain my curiousity , so I looked into that sunroof again last night - found a couple loose rivets swimming around the back. The sagging rear clamping rail(no rivets left on it) is Definitly what is jamming the sunroof movement. The seal itself came out in one piece no problem.
Is riveting that clamping rail a DIY job ? If so I imagine the whole roof panel needs to come out,is there a specific rivet to use ?