I wish I could help you on those questions.

When a rear light cluster fades, polishing won't bring back the color. I just buy a new one. Generally they are available and not too expensive, thanks to fender benders.

As for frosted headlights, I bet you're referring to the plastic aero lights Volvo started using in the late 80s. The light they throw is so bad that I look for any excuse to junk them. I fit in Euro lamps or older US light buckets assemblies where you have individual replaceable lights.

Mercedes US lamps might not be as good as their Euro lamps, but at least they always threw decent light and didn't frost up badly after a few years of use. The lights on my US 560SEL were original and worked OK for DOT lamps. I melted the bulb connectors with hi-watt bulbs, but replacing them with higher-quality connectors solved that problem.

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Thx/Reno
An American in France
88 300TD 5spd Sportline (lowered factory susp) - totalled by a flying deer
89 Range Rover V8 - the 4wd beast
02 Toyota minivan
05 Peugeot Partner 4x4 Dangel
88 International Harvestor 633SA
--Gone but not forgotten:
1970 250/8 C (sold to buy 450 SLC)
1972 450 SLC (sold after battling wiring harness problems too long)
1971 300 SEL 6.3 (sold after destroying two *very* expensive rear LS diffs)
1986 560 SEL (now my little brother's pride and joy)