If you manage to find a workable D3 fob replacement please let us all know.
I expect there are many D3's owners with FOB's that look like filigrees, with all the rubber broken down.
I purchased a "replacement" Fob case from Hong Kong on Flea Bay, and just put it straight into the bin.
It was hard plastic and impossible to use around existing electronics.
There is the scary do it yourself video.
https://www.youtube.com/watch?v=RM6SzJ3e4uE
with a cover (below) at a cheap price....
Fits RANGE ROVER Sport Land Rover Discovery 3 BUTTON REMOTE KEY FOB CASE | eBay
But after my first purchase, I am wary of the aftermarket covers and get by with some silicone to seal the holes and some care using the key.