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The reflector is being dust off, poor quality from sylvania, OK 20 year old unit... my 40 year old motorcycle with daylight running light, still has a perfect reflector!

AFAIK it's actual silver applied to the glass. I'd think it would have to oxidize to peel off. The bulb was evacuated initially, and maybe the seal has been breached. Thus only nominally a "sealed beam." The filament is in its own sealed capsule inside the bulb (filled with inert gas doped with a halogen).

I happened to have just dropped one of these and found the lens/reflector interface is actually a sealant and the lens had no trouble separating from the reflector when the reflector broke. I think Tim's right and your's has leaked though I suspect it started with an inert purge rather than being evacuated.

The good thing is I now have a small high power test light.

Yeah, likely so - argon is cheap. About 1% of the atmosphere, and it liquefies at temps between oxygen and nitrogen: a byproduct of making liquid air.

I found both my headlights needed new adjusters. When the new ones arrived, I was taking the bulbs out to install adjusters on the buckets, and when the chrome trim ring came off the outside of the lip, the actual face lens came off with it. Apparently from sitting for 18 years facing into the noon sun, the seal of the lens to base dried out, and turned to powder. Lights still work, but replaced them, as they should be "sealed".