I thought I would throw this into the mix...
I ran into Colin Skeaping at Comikaze last October in LA. He was Mark Hamill's stuntman for the original trilogy. He swore up and down, 100% positive, adamantly affirming that the strips were rubber. The prop guys on the set told him they were (and I quote) "tank wiper blades". Of course, tanks don't usually have windows, but I could give the prop guy the benefit of the doubt and believe he exaggerated a bit and that they were wiper blades from some heavy military vehicle with windows. I take it with a grain of salt, but he was there and I was not. Also, he held the original props and I did not. Also, he talked with the prop guys on set and I did not. So...for what it's worth.
I'm sure Skeaping is accessible for further questions about this (he would probably love the attention) and does anyone think it would be worth reaching out to any of the surviving prop department personnel for answers? I'm sure they would gladly tell what they know.