Plastic will Oixidize, also become brittle, do not try gasoline to clean. If you think your Lighting is Dipped/Poor then do some steps
1 change the bulb, not sure the Bulb of the car, look it up in the books in front of you at the auto store, or on-line
2. if the lighting is still dipped/poor after a replacement was in, check the battery, another sign of weak batteries is by the draw.
3. if the housing is the issue you will need to clean the outside first with the correct kits, if the inside is the issue, then by all means replace.