The glass part is literally the lens, which sits in front of the bulb. The plastic surround is a heavy lexan type material which does get cloudy with age. Also develops cracks as well. The lens is bonded to the reflector assembly in US cars. This is the part of the headlight assembly that fits in the bucket which adjusts where your headlights are aiming.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.