Yes i have one of those type keys.rodsfromday,
Since the transponder is not soldered to the board it sounds like you have the old (rubber button/replaceable battery) key fob and not the newer diamond key then.
Are you sure the unlock button is not working and it's not a general module problem? Watch the interior lights when pressing unlock. If the lights come on then the button is fine and it's the general module door lock relays are bad.
To answer your original question. Yes, transfering the guts from another, similar style, BMW key would work just fine. If you buy one from another country make sure the frequency is the same. The options are 315MHz or 433 MHz if I remember correctly. It'll require a quick key resync and you're good to go.
Thanx i was thinking of that but i tested my battery last night and it reads 3.1V. It might drop of with the 'load' but i will look into it!! I will pick one up when i go to the 'city' in the nest few weeks!Rod, I had the same issue with my (non diamond) key, it locked but only unlocked on the odd occasion. Simply changed to a new (good) battery and problem solved! BTW buy a good battery not a crap brand as I tried and it still had the same issue Energizer (expensive but works)