My yellowing was not the lens of the headlight assembly, but rather the actual plastic that light up when the halos are on. Mine yellowed horribly. You only see the yellowing when the lights are off, so my car looked horrible when parked or the halos were off.
09 SG E90, Black on Carbon Leather, Tech, Premium, Cold, iPod, Premium Sound, 19s, OEM Alarm, PDC, Moonroof, Sirius
Eisenmann Sport / Eibach Springs / 35% F1 Pinnacle Tint / Macht Schnell Air Filter / LUX Angel Eyes / Black Grill / AA Pulley / Powerchip Stage II Tune / Fabspeed X-Pipe & HFC / RAC Monolites RG63