Also, his auction says that it has a 6-year "exterior durability." This makes me wonder .... my original one looked great for about 20 years, before the clear parts started looking chalky. If these new ones maybe last a lot less time, maybe we should be looking for the ones that have only the letter outlines (without the clear "filling" inside the letters)?
Let's clear up some misunderstanding here.
The vinyls you are looking at on ebay, at least the ones Dave linked above, are all die cut vinyls which means they ARE the type without the clear filling as you refer to it. So with the type of material that particular seller is using, he estimates it will hold up well for at least 6 years.
I believe the banners George was selling, and may sell again at some point were die cut as well. Though I'm pretty sure Georges had better attention to detail. I'll elaborate on that in another post.
The TOR Parts ones I linked, which are considerably more expensive, have the colors printed over a clear vinyl backing like the OE sticker. Maybe it would hold up 20 years depending on conditions, maybe not. There's no way it's the exact same material as Toyota was using in the 80's. You could email them if you are concerned about lifespan I'm sure they'll answer what they can.
The clear backing makes for a lot less edges, nooks and crannies to clean when detailing so that might be a selling point too.
Personally I will be going for the clear backed sticker after painting, and that's coming from someone with a die cut banner currently.
-DISCLAIMER- I have never seen a picture of the TOR Parts banner on a car, so I can't confirm the accuracy of it, though I have faith in those guys. They take Toyota restoration seriously. If anyone has one please chime in I would love to hear a review.