OK, I'll jump back in. I'm not a trained mechanic or a LR expert, caveat emptor. I have worked on many different cars, mostly back in the early '90s when I ran an autolube and repair chain with my family in Santa Barbara, CA. That said, the whine in the different, transmission, or transfer case - aside from a normal sound - is the result of uneven or excessive wear. Often that comes from not enough fluid or not changing the fluid often enough. When that happens the gears and metal parts aren't bathed enough in the lubricant resulting in metal that can be broken off. In addition, the gear oil helps to keep the metal parts cool and dissipate heat. This is why it's recommended to get your gear oils changed in the first 500-1000 miles of ownership, to remove the metal debris created from the wearing together of the gears. Although that is more critical in the engine itself.
But, that should not continue to happen over time unless something fails or goes wrong - or wears out. Once you have that metal wear and debris in the gear box it's only a matter of time before something more serious fails. From a warranty and longevity perspective it makes the best sense to replace the whole gear box and start over.
That's my explanation, for any that benefit, of why the gear boxes would need to be replaced instead of a part or the fluid in them, once you've reached that point. Take it for what it's worth.
Based on my experience I would definitely have all the gear boxes and fluids checked. If the dealership serviced all of them and there are concerns about the quality of that service job and the results, you need to have a serious conversation with them and let them try to resolve the situation to your satisfaction. Good luck!
