[ainarssems]

I think it's a cost cutting measure moving from rubber/foam thingy to butyl, to permanent seal.

If you look at older headlights with glass lenses including PF 8 they all had foam/rubber seals and clips holding them on for easy of replacement if glass brakes. But you rarely see lights with glass lenses having wate/condensation. Move to plastic/polycarbonate was to reduce manufacturing cost, weight and damage/replacement needs but at first still used old method of rubbery gasket and clips. But they are extra parts parts that need to be manufactured and fitting and logistics support so they moved on to butyl which can come in a roll or just heated up and squeezed out of nozzle. They still kept clips, presumably too hold on lenses even if gets hot. Later still they moved on to permanent sealant, similar stuff to windscreen sealant, often called PermaSeal, still kept clips out of habit or possibly to keep lenses in place while sealant sets. But more recent lights get away without clips alltogether as another cost saving, maybe enabled by faster setting sealants. You still get water/condensation with PermaSeal, I don't know what the reason is but I don't think it's the lens seals.

I have done replacements on both butyl and PermaSeal, butyl is a bit messy but not too hard and PermaSeal is a bit more challenging. I have pair of lenses for Q7 headlights waiting to be fitted but I just keep coming with excuses and delaying it as not looking forward to dealing with permanent sealant.