Are the new ones the same material? I didn't think the original decoys worked as erasers. I certainly haven't tried with any of mine at least.I have a few of the Autobots at the moment and they don't look to have deteriorated at all. Just don't let them get dirty, or put in an environment/storage where they could get marks on them. Stuff like pen marks might be impossible to remove from that kind of rubber.
I have a G1 TF eraser that seems to have survived quite well loose, if that helps. The material feels more dense than the soft rubber of the decoys though.