Latest revision CANBUS Gateway for golf mk5 is 1K0 907 530 ''S'' .This apparently cures the battery drain issue upon either installing a version C rns 510 or doing the f/w 2660 update to earlier revisions.
So if you are considering the firmware update or buying a version C then my advice would be to avoid this happening check the gateway or to be safe get the gateway changed and firmware updated at the stealers, then if it goes tits up its not your problem.