I have the same issue with used ones and all the polished aluminum trim in my suburban interior
You could clear coart but it takes away from the shinyness of the aluminum
I bought new Telstar and there no comparison to the finish on a used one, but the new one will get the same dullness over time (ven with the ideal environment)
I'm currently having CAD files constructed for a lunar replica base cone
Depending on price for CNC manufacturing, I might make complete replica lamps available in other options than just polished aluminum,
Chromed Plated (single)
this will eliminate polished aluminum from oxidizing
What's so bad about the finish on the new Telstars?
My Telstars are of circa-2000 vintage and develop a strange dark patina on the legs, which is a real pain to polish off. I remember hearing that the newer post-reintroduction models didn't suffer this problem, but I'm not sure.
Anyway, I second the idea of a good quality car wax/ polish - something not too abrasive, which should 'seal' the finish, for a while anyway. I used Auto-Glym super-resin polish last time, which seemed to work quite well (quite expensive to buy though)