Sorry to hear that! I went through something similar, just with ADH warranty.
When my replacement unit arrived, I found no trouble at all authorizing it to my Reader account - just authorize and recopy my library.
Now that has used my fourth slot - 2 computers, and this was the second Reader. The first reader doesn't have the "deauthorize" option, but I believe that if I ever need the slot I won't have a problem after contacting connect support. But I'm waiting until I need that as a sixth slot. It shouldn't be a problem unless you're already up to six.
Whether or not it's worth a fix price of $288 to you I don't know....