I'm not sure if this is better suited for the TA thread or this one.... but on my '02 x-star the Air vent grill things not sure what to call them - (one on each side of hull just before the windscreen.... they are plastic held in with two screws).
Mine were yellowing.... sprayed a shot of Totally Awesome on them and the spray turned dark yellow and to my surprise when I wiped... The grill was stark white!
I then went out side and sprayed some on my wifes headlights that fogged from the sprinklers and voila! Same effect spray turned a dark yellow and the lights were sparkling again!