I'm not trying to defend BMW and I have no affiliation with them but here is my take on the situation.
The bottom line with goodwill repairs is that if they think it will get you to buy a new or CPO from BMW at a later date they'll be more inclined to do it. If they don't see any benefit to them then they won't. If you had bought it from United (new or CPO) we probably wouldn't be having this conversation.
You may be the one person that would have come back at a later date and bought a BMW. But there are many, many, more that are just looking to get BMW to fix a car that they bought used somewhere else and heard about the goodwill program. BMW has to draw the line somwhere or they would be taken for chumps and go broke fixing used BMW's for free.
A bad sunroof seal is a time issue so low mileage doesn't matter. If the car has been parked in the searing Atlanta sun since it got off the boat then a bad seal is not unheard of. My X3 is only outside when I'm driving it for this very reason. Otherwise it stays out of the elements in my garage.
If you want to try to fix it yourself I found some info you might find helpful:
http://www.bimmerfest.com/forums/sho...d.php?t=496666
Part numbers can be found here:
http://www.realoem.com/bmw/partgrp.d...id=49511&hg=54
The factory shop manual calls for Terokal 2444.
http://loctite.fast.de/no/Teroson/Terokal-2444.htm