Time to trade it in guys (kidding). I believe I’ve seen another MKVII Jetta owner with this problem either on here or Vortex, couldn’t find the thread. I know my mother in laws Jetta has this cracking also. I noticed it on hers first, and paid special attention to my wife’s car in the way of keeping this area clean and “conditioned” with a uv inhibiting spray wax. I noticed yesterday while washing the car, that it has started cracking as well.
At this point the cracks are small, but I wonder as the car ages if they will get to the point where they allow water intrusion. When the door closes it pushes slightly back on this rubber strip forming a seal. I suppose the constant pressure of the door pushing back on this area eventually causes it to split. Unfortunately it is part of the quarter panel glass so the whole unit would need replacement. Maybe this would be a good candidate for an end of warranty replacement.
At this point the cracks are small, but I wonder as the car ages if they will get to the point where they allow water intrusion. When the door closes it pushes slightly back on this rubber strip forming a seal. I suppose the constant pressure of the door pushing back on this area eventually causes it to split. Unfortunately it is part of the quarter panel glass so the whole unit would need replacement. Maybe this would be a good candidate for an end of warranty replacement.