Do not use ATF.
While the original Texaco fluid may be nearly impossible to purchase in individual bottles, Land Rover offers a comparable fluid through dealerships. Some dealership employees are unaware of this fluid.
It isn't the cheapest fluid you'll ever buy, but you should either use this or another fluid that comes close to matching it. Some higher-end aftermarket fluids will work, but I cannot remember which is which.
I did a lot of research to find other options, but I've managed to lose the file and forget all of it. I'll sort it out again sooner or later.
ATF is not the answer. I have personally experienced it's effects in a number of used Land Rovers, and even accidentally used it in my own DII once. I don't know what the fuck I was thinking when I did that.
Noise began shortly thereafter, and once I realized that I'd made a damned fool mistake, the issue was cured immediately by flushing it all out and filling with appropriate fluid.
Cheers,
Kennith