I had my lumbar support do that back in the end of February. I wasn't aware of a TSB about it and wasn't told by the dealer. Anyway, they had the vehicle for one day, had the seat out and didn't have the bolts to fix it (it's a spring held by bolts that expands -- I always thought it was an air bladder, especially since i heard the loud pop). Now it's going back in tomorrow now that the parts are in. It is NOT a 30 minute fix according to my dealer, but an all-day repair. They will have a loaner ready for me this time. Apparently, they remove the seat out of the vehicle (you'll lose your saved seating positions), and must disassemble the back to access the lumbar part in question.
Good luck and let me know if your dealer does it in 30 minutes. BTW, my Terrain was a 36500 KM when it went (though the vehicle is only 9 months old).