Hello, on peugeot 106 keyfob (single large button) I had the problem of the button membrane dropping off .

Peugeot garage said I had to buy a complete key. When I asked to see the exploded view of the key you could see which parts were detailed seperately and available. And yes the membrane could be ordered.

Yes on Ebay you can buy keys (old & new) and key membranes. The metal keypart can be swopped over but the electonics might need to be reprogrammed. If you just want the black plastic bit you can swop over the electronic bit. But the price is high if you just want the Black plastic bit.

Watchout for Ebay 'key' sellers. Before I bought the new membrane I bought a 2nd hand key with a good membrane but it had to be reprogrammed to my car. The sellers offer Programming instructions but are very dependant on model and sometimes year. Never got the correct instructions to program the key and sent it back (Cost £30).

PS whilst I was trying to program the 2nd hand key my original key was sitting in the ignition key to give electric to the sensor behind the mirror. My original key became unprogrammed !! Managed to program it back though.