usually if they're just a little dull, you can clear coat them
i just bought a aus spec tailight from scott (rol-110) with the amber signal lens.
here in the u.s. amber wasn't legal on the rear until '76 so they were all red
the right side lens i bought off ebay was REALLY faded, chipped, scratched, and just sun eaten.
scott's was nice except the clear lens, but i had a nos one anyway
i've sprayed thin coats of a metallic red before, but i just found this new product....
it's to be sprayed over bare aluminum/steel/silver paint to resemble an anodized look, but the pigment is so thin, it works perfectly for lenses
they even have it in orange to restore amber lenses!
i don't know if they have this there in aus, but it's worth a look
just clean the lens and scuff it with 800 grit wet/dry, then spray
i didn't use a clear primer, and i don't know if it will fade, but it has a guarantee...
guess which one had the amber t/s.......