I found a tsb on that, click here. It says to install a new sealing patch part #15820928
Genuine GM BARRIER Replaced by: 25982597Your Price: $2.81
The tsb said you will need 2.
They are calling the fascia part #24 in this diagram.
#22 is a pop rivet for the fascia bracket
#21 is a fascia bolt/screw
#20 is a fascia retainer
#11,12 and 13 are also a stud, nut and bolt for the fascia