XC70: General Spider web cracks in headlight casings

[XCR]

I've only ever used sealants and waxes on any I've restored with long lasting results. I'll look into it further though.

[ferg55]

Your waxes and sealants probably have a UV inhibitor, so effectively they are doing the same thing as a lacquer, albeit less permanent.

I'm not sure the lenses were coated by the manufacturer, I used to work for a firm which manufactured the rear lamps for various marques, and another which made the exterior rear view mirrors for Volvo, JLR etc which incorporates the small clear indicator lens - none were coated, instead the raw plastic material used for these sorts of products has a UV inhibitor mixed into it. Any inhibitor is only effective for a period of time, maybe 10 or20 years depending on % added. So I think what is more likely happening is that when you sand and polish the lenses you inevitably leave many microscopic scratches in the surface and these accelerate the UV degradation. That said, I'm not sure why stone chips don't seem to do the same thing - my 260k mile 2007 S80 has the usual array of chips on the lenses but no hint of yellowing.