Transfer Box Additive

Hi, I have a 2.5 petrol 90 (well someone has to) with quite a loud whine comming from the transfer box, sounds just like a dry bearing, is speed dependant and not load dependant. Local landrover man says "worn bearing and best to live with it, might try a gearbox additive".

Has anyone any experience of gearbox additives, I am told teflon based ones are best and could help reduce noise

thanks ..... Richard