Well, I finally worked up the nerve to take the key apart (I was afraid I was going to break it, but I finally figured out how it fits together). I noticed that it didn't have a battery in it at all (Maybe it fell out at some point? The screw is missing, too..... Hmmm). I went to my local Wal-Mart and picked up a couple of CR1216 batteries, popped one in, and now the key works fine. I've read that the key loses its programming after a long period of not having a working battery in it, but that appears to not be the case with me ES300. Anyway, thanks for the help! :)
Good luck arutha, let us know how the fix goes. B)
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