Last night my fob stopped working, replaced batteries today, have tried to reset as per many threads on here, but still not working. dont want to reprogramme second key as suggested as its working fine at the moment any idea's please

Hello Looking for some help and advice, I am considering buying a Range rover, hopefully if funds allow a 3L TDV6.About an 02 or 03 plate. Are there any known problems that i should be looking for, Is the auto gearbox one of those sealed for life jobs. Thanks for any replys