Key Fob shells are available on the bay, no problem. Prise the back off as if you were changing the battery and you should be able to carefully prise out the circuit board and drop in into place in the new case, it's held in place by some tiny clips at the edge of the board. The key blade is a tight, very tight fit into the fob. Pull it out of the old case and push it back into the new one. You'll probably have to grip the key blade in a vice, so be careful not to bend it, but it can be done.