FWIW, all the [undamaged] alum. ones I've noticed Vs GPA's 26420 is the former all look like alum. with a slight golden color from a fungus proofing coating [based solely on what we use to spray, dip or brush on various types of electrical/electronic components, assemblies] that's pretty obvious from the dome's backside whereas the [2] 26420 have a slightly milky looking and decidedly mottled, coating, ie. almost cheap plastic looking. Otherwise, the only way I would know is by finding out the expensive way with high power testing.

GM