Are you talking about the rubber rain channel/gasket above the headlight? Mine has broken tabs on the right side, too haha.
Or, is it on the lens itself somewhere? If it's that, then a tab being broken causes no problems with the headlight. Explain to them that the headlight lens is glued, and requires temperatures up to 350 degrees to soften the glue and separate. It is water-tight and the tab has very little contribution, if at all, to the integrity of the lens. Shoot, even spray a hose on the headlight and show them it's water-tight, therefore a broken tab doesn't mater.
E46Fanatic's resident mathemagician