my wife drives a 2011 MKX (same basic SUV) and it is currently at the dealer getting the sun roof fixed for the exact same problem- fortunately for me its a warranty issue and I am not paying for it, my understanding is that it is the tracks that are the problem and they are replacing them. Apparantly it's a fairly big job as they will have the car for a few days (dropped it off Thursday and don't expect it back till Tuesday). A mecaninc was standning there when I dropped it off, and he acted like this is a fairly common problem with these cars.
I'll update you when I pick up the car and find out exactly what they had to do.
ET: 12.7@109 mph
FiTech EFI, DSS 347, AFR 185s, Vic Jr, XE274HR cam, MSD ign, Hooker Headers, Magnaflow exhaust
Tremec 3550, Pro 5.0, Fidanza AL Flywheel, McCleod clutch, 3.55's, 13" GT Front & Cobra Rear brakes
17" TTII's, 235/45 tires, 620 coils, Shelby drop, 1" & 3/4" sway bars, Monte Carlo bar, S&T strut rods, Bilsteins, & roller perches