Sorry to hear, CookieMonster. Be polite but firm- you should let them know from the outset that one way or another, they will have to fix it.
It does seem to be surprisingly common. Enough for me to think very carefully before buying a car with a sunroof.
I’ve had 2 Bmws and currently a Seat Alhambra with a pan roof, never had any problems of any kind.
I wonder also if this happens more often in cars parked outdoors during winter months?