John, it can be done without dropping the AC- casing.
The louvre itself with som TLC can be pulled out. (turning/wiggling with some long pliers.)
On either side of the louvre is a hinge pin approx 1/4 dia .on either of this pins belongs a small springtype washerring.
These might be fallen in the casing..( with flashlight you should be able to find.)
The louvre swivels on 2 holes left and right in the casing.
Its a not too difficult job, its selfexplaining.
succes
Mark