So all done.
Ordered and recieved a generic Key case off Amazon. Its plastic as plastic is, reasonably robust and the swop over of the internal circuit board quite straightforward, used the original fob back piece which clipped onto the new fob button front fine so didn't even have to mess about with transferring the transponder.
Bought a loctite super glue pen that advertised suitable to use on plastic for £3 and the key blades on both my keys are now both rock solid.
https://www.amazon.co.uk/dp/B01LCHCU...841_TE_3p_dp_1